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FLU_SHOT+, Version 1.84 A Form of Protection from Viral and Trojan Programs by Ross M. Greenberg and Software Concepts Design Post Office Box 908 Margaretville, New York 12455 BBS:(607)-326-4425 1200|2400|N/8/1 Voice: (607)-326-4422 Fax: (607)-326-4424 _______ ____|__ | (TM) --| | |------------------- | ____|__ | Association of | | |_| Shareware |__| o | Professionals -----| | |--------------------- |___|___| MEMBER FLU_SHOT+ is a trademark of Software Concepts Design. Copyright (C), 1988-1990 by Software Concepts Design. All Rights Reserved. Not for Commercial Distribution without written permission by the copyright holder. Noncommercial copying of this software and this documentation is encouraged. Commercial Distribution is easily defined: if you distribute this software, or the enclosed documentation, for more than your cost of such distribution, then you're a Commercial Distributor and require our written permission. Not-for-profit organizations and computer user groups, and their bulletin board systems (if any) are specifically *not* considered commercial distributors. By your using this software, you agree to the terms herein. Specifically, that you do not have the right to copy this software except as outlined above, and that you are granted a license to use this software only by registering this software as mentioned elsewhere in this document. You also agree, and signify that agreement by using this software, that Software Concepts Design and Ross M. Greenberg will not be held liable for any reason for any cost you may incur, or any potential income you might lose as a result of using this software. Finally, this software is provided "AS IS", meaning that what you see is what you get. If you use this software and a tree falls on your house, or your spouse leaves you for someone younger and more virile, please do not bother having your lawyer call -- it isn't the fault of the software, no matter what the lawyer tries to convince you! Maybe lawyers should all work on a shareware basis: they only get paid if you're satisfied with their work? One can dream.... Software Concepts Design can be reached by the following means *by*registered*users* of FLU_SHOT+: Telephone: Monday-Friday, 9am - 5pm (EST): 607-326-4422 RamNet BBS: 607-326-4425 MCI: 'greenber' BIX: 'greenber' CompuServe: [72461, 3212] Table of Contents I. Introduction a. What is a Trojan.....................................1 b. What is a Virus......................................4 c. The Challenge to the Worm............................6 II. About the FLUSHOT Series a. A Brief History......................................8 b. FLU_SHOT+ Features and Enhancements..................9 c. Registering FLU_SHOT+................................10 d. Site Licensing of FLU_SHOT+..........................10 III. Using FLU_SHOT+ a. Down and Dirty Installation: Step-By-Step............12 b. The FLUSHOT.DAT file.................................14 1. Protecting files from Write Access..............15 2. Protecting files from Read Access...............15 3. Excluding files.................................15 4. Checksumming files..............................16 5. Registering a TSR program.......................17 6. Restricted Access...............................17 7. Protecting the FLUSHOT.DAT file.................18 8. Protection Recommendations......................18 9. Allowing "dangerous" programs to run............19 10. Protecting your Boot Track......................19 c. Running FLU_SHOT+....................................20 1. Checksumming the in-memory table................20 2. Intercepting Direct Disk Writes Through INT13...21 3. What about INT26................................21 4. Turning off the header message..................21 5. Disabling Triggering on Open With Write Access..21 6. Changing the Trigger Window Attributes..........21 7. Allowing trusted TSR's to work..................23 8. Disabling FLU_SHOT+.............................23 9. Disabling FLU_SHOT+ Toggle Display..............24 10. Forcing FLU_SHOT+ to only use the BIOS..........24 10. Defining the "Special" Keys.....................25 11. Putting FLU_SHOT+ to sleep when run.............25 IV. Interpreting a FLU_SHOT+ Trigger..........................26 V. How Good is FLUSHOT+, Really?.............................30 VI. Reward Offered............................................31 VII. Appendices Appendix A: Common Questions and Their Answers...........33 Appendix B: How Does A Virus Work?.......................38 Introduction What is a Trojan? ================= Back in the good old days (before there were computers), there was this bunch of soldiers who had no chance of beating a superior force or of even making it into their fortress. They had this nifty idea: present the other side with a gift. Once the gift had been accepted, soldiers hiding within the gift would sneak out and overtake the enemy from within. We can only think of the intellectual giants of the day who would accept a gift large enough to house enemy soldiers without checking its contents. Obviously, they had little opportunity to watch old WWII movies to see the same device used over and over again. They probably wouldn't have appreciated Hogan's Heroes anyway. No color TV's -- or at least not ones with reliable reception. Consider the types of people who would be thrilled at the concept of owning their own rough hewn, large wooden horse! Perhaps they wanted to be the first one on their block, or something silly like that. Anyway, you're all aware of the story of The Trojan Horse. Bringing ourselves a bit closer to the reality we've all grown to know and love, there's a modern day equivalent: getting a gift from your BBS or user group which contains a little gem which will attack your hard disk, destroying whatever data it contains. In order to understand how a potentially useful program can cause such damage when corrupted by some misguided soul, it's useful to understand how your disk works, and how absurdly easy it is to cause damage to the data contained thereon. So, a brief technical discussion of the operation of your disk is in order. For those who aren't concerned, turn the page or something. Data is preserved on a disk in a variety of different physical ways having to do with how the data is encoding in the actual recording of that data. The actual *structure* of that data, however, is the same between MS-DOS machines. Other operating systems have a different structure, but that doesn't concern us now. Each disk has a number of "tracks". These are sometimes called cylinders from the old type IBMer's. These are the same people who call hard disks DASDs (Direct Access Storage Devices), so we can safely ignore their techno-speak, and just call them tracks. Tracks can be thought of as the individual little grooves on an audio record, sort of. Anyway, each track is subdivided into a number of sectors. Each track has the same number of sectors. Tracks are numbered, as 1 are sectors. Any given area on the disk can be accessed if a request is made to read or write data into or out of Track-X, Sector Y. The read or write command is given to the disk controller, which is an interface between the computer itself and the hard disk. The controller figures out what commands to send to the hard disk, the hard disk responds and the data is read or written as directed. The first track on the hard disk typically will contain a small program which is read from the hard disk and executed when you first power up your machine. The power up sequence is called "booting" your machine, and therefore the first track is typical known as the "boot track". In order to read information from your disk in a logical sequence, there has to be some sort of index. An unusual index method was selected for MS-DOS. Imagine going to the card index in a library, looking up the title you desire, and getting a place in another index which tells you where on the racks where the book is stored. Now, when you read the book, you discover that only the first chapter of the book is there. In order to find the next chapter of the book, you have to go back to that middle index, which tells you where the next chapter is stored. This process continues until you get to the end of the book. Sounds pretty convoluted, right? You bet! However, this is pretty much how MS-DOS does its "cataloguing" of files. The directory structure of MS-DOS allows for you to look up an item called the "first cluster". A cluster represents a set of contiguous ("touching or in contact" according to Random House) tracks and sectors. It is the smallest amount of information which the file structure of MS-DOS knows how to read or write. Based on the first cluster number as stored in the directory, the first portion of a file can be read. When the information contained therein is exhausted, MS-DOS goes to that secondary index for a pointer to the next cluster. That index is called the File Allocation Table, commonly abbreviated to "FAT". The FAT contains an entry for each cluster on the disk. An FAT entry can have a few values: ones which indicate that the cluster is unused, another which indicates that the associated cluster has been damaged somehow and that it should be marked as a "bad cluster", and a pointer to the next cluster for a given file. This allows for what is called a linked list: once you start looking up clusters associated with a given file, each FAT entry tells you what the next cluster is. At the end of the linked list is a special indicator which indicates that there are no more clusters associated with the file. There are actually two copies of the FAT stored on your disk, but no one really knows what the second copy was intended for. Often, if the first copy of the FAT is corrupted for some reason, a clever programmer could recover information from the second copy to restore to the primary FAT. These clever programmers can be called "hackers", and should not be confused with the thieves 2 who break into computer systems and steal things, or the "worms" [Joanne Dow gets credit for *that* phrase!] who would get joy out of causing you heartache! But that heartache is exactly what can happen if the directory (which contains the pointer to the first cluster a file uses), the FAT (which contains that linked list to other areas on the disk which the file uses), or other areas of the disk get corrupted. And that's what the little worms who create Trojan programs do: they cause what at first appears to be a useful program to eventually corrupt the important parts of your disk. This can be as simple as changing a few bytes of data, or can include wiping entire tracks clean. Not all programs which write to your hard disk are bad ones, obviously. Your word processor, spreadsheet, database and utility programs have to write to the hard disk. Some of the DOS programs (such as FORMAT), if used improperly, can also erase portions of your hard disk causing you massive amounts of grief. You'd be surprised what damage the simple "DEL" command can do with just a simple typo. But, what defines a Trojan program is its delivery mechanism: the fact that you're running something you didn't expect. Typical Trojan programs cause damage to your data, and were designed to do so by the worms who writhe in delight at causing this damage. May they rot in hell -- a mind is a terrible thing to waste! Considering the personality required to cause such damage, you can rest assured that they have few friends, and even their mother doesn't like to be in the same room with them. They sit back and chortle about the damage they do with a few other lowly worms. This is their entire social universe. You should pity them. I know that I do. 3 Introduction What is a Virus? ================ Trojan programs are but a delivery mechanism, as stated above. They can be implemented in a clever manner, so that they only trigger the malicious part on a certain date, when your disk contains certain information or whatever. However they're coded, though, they typically affect the disk only in a destructive manner once triggered. A new breed of programs has the capability of not only reserving malicious damage for a given event's occurrence, but of also replicating itself as well. This is what people refer to when they mention the term "Virus Program". Typically, a virus will spread itself by replicating a portion of itself onto another program. Later, when that normally safe program is run it will, in part, execute a set of instructions which will infect other programs and then potentially, trigger the Trojan portion of the program contained within the virus. The danger of the virus program is twofold. First, it contains a Trojan which will cause damage to your hard disk. The second danger is the reason why everyone is busy building bomb shelters. This danger is that the virus program will infect other programs and they in turn will infect other programs and so forth. Since it can also infect programs on your floppy disks, you could unknowingly infect other machines! Pretty dangerous stuff, alright! Kenneth van Wyck, one of the computer folks over at Lehigh University, first brought a particular virus to the attention of the computer community. This virus infects a program, which every MS-DOS computer must have, called COMMAND.COM. This is the Command Line Interpreter and is the interface between your keyboard and the MS-DOS operating system itself. Whatever you type at the C> prompt will be interpreted by it. Well, the virus subverts this intended function, causing the infection of neighboring COMMAND.COMs before continuing with normal functionality of the command you typed. After a certain number of "infections", the Trojan aspect of the program goes off, causing you to lose data. The programmer was clever. But still a worm. And still deserving of contempt instead of respect. Think of what good purposes the programmer could have put his or her talents to instead of creating this damage. And consider what this programmer must do, in covering up what they've done. They certainly can't tell anyone what they've accomplished. Justifiable homicide comes to mind, but since the worms they must 4 hang around are probably as disreputable as they are, they must hold their little creation a secret. A pity. Hopefully, the worm is losing sleep. Or getting a sore neck looking behind them wondering which of their "friends" are gonna turn them in for the reward I list towards the end of this document. 5 Introduction The Challenge to the Worm ========================= When I first released a program to try to thwart their demented little efforts, I published this letter in the archive (still in the FLU_SHOT+ archive of which this is a part of). What I say in it still holds: As for the designer of the virus program: most likely an impotent adolescent, incapable of normal social relationships, and attempting to prove their own worth to themselves through these type of terrorist attacks. Never succeeding in that task (or in any other), since they have no worth, they will one day take a look at themselves and what they've done in their past, and kill themselves in disgust. This is a Good Thing, since it saves the taxpayers' money which normally would be wasted on therapy and treatment of this miscreant. If they *really* want a challenge, they'll try to destroy *my* hard disk on my BBS, instead of the disk of some innocent person. I challenge them to upload a virus or other Trojan horse to my BBS that I can't disarm. It is doubtful the challenge will be taken: the profile of such a person prohibits them from attacking those who can fight back. Alas, having a go with this lowlife would be amusing for the five minutes it takes to disarm whatever they invent. Go ahead, you good-for-nothing little slimebucket: make *my* day! Alas, somebody out there opted to do the cowardly thing and to use the FLUSHOT programs as a vehicle for wrecking still more destruction on people like you. The FLUSHOT3 program was redistributed along with a companion program to aid you in reading the documentation. It was renamed FLUSHOT4. And the reader program was turned into a Trojan itself. I guess the programmer involved was too cowardly to take me up on my offer and prefers to hurt people not capable of fighting back. I should have known that, I suppose, but I don't normally think of people who attack innocents. Normally, I think of people to respect, not people to pity, certainly not people who must cause such damage in order to "get off". They are below contempt, obviously, and can do little to help 6 themselves out of the mire they live in. Still, a worm is a worm. 7 About FLUSHOT A Brief History =============== The original incarnation of FLU_SHOT was a quick hack done in my spare time. It had a couple of bugs in it which caused it to trigger when it shouldn't, and a few conditions which I had to fix. A strangeness in how COMMAND.COM processed certain conditions when I "failed" an operation caused people to lose more data than they had intended -- certainly not my intent! FLU_SHOT was modified and became FLUSHOT2. It included some additional protections, protecting some other important system files, and protecting against direct disk writes which can be used to circumvent FLUSHOT's protection mechanisms. Additionally, FLUSHOT2 forced an exit of the program currently running instead of a fail condition when you indicated that an operation should not be carried out. FLUSHOT2 was also now distributed in the popular archive format (have you remembered to send your shareware check into Phil Katz for his efforts? You really should. It ain't that much money!). Next came FLUSHOT3. A bug was fixed which could have caused certain weird things when you denied direct disk I/O to certain portions of DOS 3.x. The enhancements to FLUSHOT3 included the ability to enter a 'G' when FLUSHOT was triggered. This allowed FLUSHOT to become inactive until an exit was called by the foreground task. So, when you used some trustworthy program which did direct disk I/O, you wouldn't be pestered with constant triggering after you enter the 'G'. Primarily this was a quick hack to allow programs such as the FORMAT program to run without FLUSHOT being triggered each time it tried to do any work it was supposed to. 8 About FLUSHOT FLU_SHOT+ Features and Enhancements =================================== This release of FLU_SHOT has a new name: FLU_SHOT+. Because FLUSHOT4 was a Trojan, I opted to change the name. Besides, FLU_SHOT+ is the result of some real effort on my part, instead of being a part-time quick hack. I hope the effort shows. FLUSHOT is now table driven. That table is in a file which I call FLUSHOT.DAT. It exists in the root directory on your C: drive. However, I'll advise you later on how to change its location so that a worm can't create a Trojan to modify that file. This file now allows you to write and/or read protect entire classes of programs. This means that you can write protect from damage all of your *.COM, *.EXE, *.BAT, and *.SYS files. You can read protect all of your *.BAT files so that a nasty program can not even determine what name you used for FLU_SHOT+ when you invoked it! Additionally, you can now automatically check programs when you first invoke FLU_SHOT+ to determine if they've changed since you last looked at them. Called checksumming, it allows you to know immediately if one of the protected programs has been changed when you're not looking. Additionally, this checksumming can even take place each time you load the program for execution. Also, FLU_SHOT+ will advise you when any program "goes TSR". TSR stands for "Terminate and Stay Resident", allowing pop-ups and other useful programs to be created. A worm could create a program which leaves a bit of slime behind. Programs like Borland's SideKick program, a wonderful program and certainly not a Trojan or virus, is probably the best known TSR. FLU_SHOT+ will advise you if any program attempts to go TSR which you haven't already registered in your FLUSHOT.DAT file. Finally, FLU_SHOT+ will also now pop-up a little window in the middle of your screen when it gets triggered. It also will more fully explain why it was triggered. The pop-up window means that your screen won't get screwed up beyond recognition -- unless you're in graphics mode when it pops up. Sorry, 'dems the breaks! This version, FLU_SHOT+, has some other substantial improvements on the security side, has a couple of bug fixes here and there and is generally the same program - just a little more reliable, and a little more user friendly. And, more closely attuned to what you, the user community, have asked me for. More information about FLU_SHOT+ and its enhancements can be found in the file "UPDATES.TXT", in the archive. My thanks to Mr. Mark Hamilton of the UK for some enhancements ideas and code. 9 About FLUSHOT Registering FLU_SHOT+ ===================== FLU_SHOT+ is not a free program. You're encouraged to use it, to distribute it to your friends and co-workers. If you end up not using it for some reason, let me know why and I'll see if I can do something about it in the next release. But, the right to use FLU_SHOT+ is contingent upon you paying for the right to use it. I ask for fifteen dollars as a registration fee, plus four dollars to meet my costs for shipping, handling, and processing each order. This entitles you to get informed when the next update is available, and to have someone available to help support you with any problem you might have with the program. And it allows you to pay me, in part, for my labor in creating the entire FLU_SHOT series. I don't expect to get my normal consulting rate or to get a return equal to that of other programs which I've developed and sell through more traditional channels. That's not my intent, or I would have made FLU_SHOT+ a commercial program and you'd be paying lots more money for it. Some people are uncomfortable with the shareware concept, or believe that there ain't no such thing as Trojan or Virus programs, and that a person who profits from the distribution of a program such as FLU_SHOT must be in it for the money. Although I sympathize with their feelings, I feel that a user of FLU_SHOT simply *must* pay for their usage of the program -- using it for free is paramount to stealing, and we know how wrong that is! I've created an alternative for these folks. I'll call it "charityware" [first called that, to my knowledge, by Roedy Green]. You can also register FLU_SHOT+ by sending me a check for $15 made out to your favorite charity. And a check made out to me for $4 to handle my costs. Be sure to include a stamped and addressed envelope. I'll forward the monies onto them and register you fully. Of course, if you wish, you can send me a check for more than $19. I'll cash it gladly (I'm no fool!). Site Licensing of FLU_SHOT+ =========================== So, you run the computer department of a big corporation, you got a copy of FLU_SHOT+, decided it was wonderful and that it did everything you wanted and sent in your ten bucks. Then you distributed it to your 1000 users. Not what is intended by the shareware scheme. *Each* site using FLU_SHOT+ should be registered. That's ten bucks a site, me bucko! Again, make the check out to charity if you're 10 uncomfortable with the idea of a programmer actually deriving an income from their work. However, if you've really got 1000 computers, you should give me a call. As much as I'd like to get $15 for each site, that wouldn't be fair to you. So, quantity discounts are available. Here's our quantity discount schedule. Remember to add in the four dollar charge for each order. Quantity Price Each ============== =============== 1 - 49 $15 + $4/order 50 - 249 $12 + $4/order 250 - 499 $10 + $4/order 500 - 9999 $ 8 + $4/order 10,000+ No Charge (after paying for 9999!) Site licensee's get a "gold" disk, and make their own copies at their site, working on the honor system. Each site license does require a separate agreement, so be sure to give us a call to work out the details. End-user contact *must* be through a single contact point in order for any of these discounts to apply. 11 Using FLU_SHOT+ Down and Dirty Installation: Step By Step ========================================= Consider this area of the manual to be the "I hate to read manuals" approach. We encourage you to read the manual, since about 90% of our tech support calls are answered by telling the caller to turn to a given page in the manual. Some people, however, just want the ability to use the product immediately, without wading through the manual. So, if you're one of those gung-ho'ers, here's a step-by-step approach: 1) If you received FLU_SHOT+ on a diskette, place that diskette in the A: drive on your system. If you received FLU_SHOT+ from a Bulletin Board System, then you've obviously figured out how to de-arc and de-compress the files contained within the archive (if not, how are you reading this?). 2) Type the following commands: COPY A:FSP.COM C:\ COPY A:FLUSHOT.DAT C:\ 3) Make C: your default drive by simply typing "C:", followed by a carriage return. Make the root directory your default directory simply by typing "CD \", followed by a carriage return. 4) Type "FSP", followed by a carriage return. This will invoke FLU_SHOT+. 5) You should expect to see three error messages. These will take one of two forms. One form will tell you that the checksum for the listed file doesn't match the actual checksum for that file. If you see this message, copy down the displayed number on a separate piece of paper, along with the filename. Press any key to continue on to the next file. 6) If you see a message indicating that a given file is not found, then you'll have to remember what the names your computer uses for the on-disk BIOS (FLU_SHOT+ expects "IBMBIO.SYS") and on-disk Disk Operating System (FLU_SHOT+ expects "IBMDOS.SYS") and edit the names in the FLUSHOT.DAT file appropriately. If, for example, your system uses the name of "IOSYS.SYS" and "MSSYS.SYS" for these files, replace the missing filenames within the FLUSHOT.DAT file to reflect the actual names you use. When you finish with these edits, reboot your system and start with step 3), above. 7) At this point, you should have three files with their actual checksums on a piece of paper. Edit the FLUSHOT.DAT file in your C:\ directory to reflect these checksums. Replace the default "[12345]" with the actual checksums you've written down. So, if the actual checksum for your COMMAND.COM file is "32767", the line in your FLUSHOT.DAT to reflect this should read: C=C:\COMMAND.COM[32767] 12 8) Reboot your system. When you invoke FLU_SHOT+, by typing FSP followed by a carriage return, everything should run to completion, leaving you at your C> prompt. 9) If you wish to cause FLU_SHOT+ to run whenever you first boot your computer, simply edit your AUTOEXEC.BAT file, found in the root directory on your "boot" drive, to include "FSP" as the last line. 10) For extra security, you might wish to rename the FLUSHOT.DAT. To do so, read the section in this manual which describes the FLU_POKE program. 11) If there are any problems in the installation procedure, it probably means that you're using something a little unique in the way of computer equipment or software packages. You'll have to read the entire document. Sorry. 12) FLU_SHOT+, "out of the box", offers some pretty good protection. If you want to substantially enhance the security FLU_SHOT+ offers you, please read the rest of the manual? Remember that we will *not* answer any tech support calls from people who have not read the manual. 13 Using FLU_SHOT+ The FLUSHOT.DAT file ==================== FLU_SHOT+ is table driven by the contents of the FLUSHOT.DAT file. This file normally exists in the root directory of your C: drive (C:\FLUSHOT.DAT). A little later in this document you'll see how to disguise the data file name, making life tougher for the worms out there. But for the purposes of this document, we'll assume that the file is called C:\FLUSHOT.DAT. The FLU_SHOT+ program will read this data file exactly once. It reads the data from the data file into memory and overwrites the name of the data file in so doing. A little extra protection in hiding the name of the file. This data file contains a number of lines of text. Each line of text is of the form: <Command>=<filename><options> Command can be any one of the following characters: P - Write Protect the file named R - Read Protect the file named E - Exclude the file named from matching P or R lines T - The named file is a legitimate TSR C - Perform checksum operations on the file named The filename can be an ambiguous file if you wish for all commands except the 'T' and 'C' commands. This means that: C:\level1\*.COM will specify all COM files on your C: drive in the level1 directory (or its sub-directories). Specifying: C:\level1\*\*.EXE would specify all EXE files in subdirectories under the C:\level1 directory, but would not include that directory itself. You can also use the '?' operator to specify ambiguous characters as in: ?:\usr\bin\?.COM would be used to specify files on any drive in the \usr\bin directory on that drive. The files would have to be single letter filenames with the extension of 'COM'. Ambiguous file names are not allowed for the 'T' and 'C' options. 14 Using FLU_SHOT+ Protecting files from Write Access ================================== Use the 'P=' option to protect files from write access. To disallow writes to any of your COM, EXE, SYS, and BAT files, specify lines of the form: P=*.COM P=*.EXE P=*.SYS P=*.BAT which protects these files on any disk, in any directory. Protecting files from Read Access ================================= Similarly, you can use the 'R' command to protect files from being read by a program (including the ability to 'TYPE' a file!). To prevent read access to all of your BAT files, use a line such as: R=*.BAT Combinations of R and P lines are allowed, so the combination of the above lines would prevent read or write access to all batch files. Excluding files =============== Programmers in particular should find usage for the 'E' command. This allows you to exclude matching filenames from other match operations. Assume you're doing development work in the C:\develop directory. You could exclude FLU_SHOT+ from being triggered by including a line such as: E=C:\develop\*.* Of course, you might have development work on many disks under a directory of that name. If you do, you might include a line which looks like: E=?:\develop\*.* or E=*\develop* 15 Checksumming files ================== This line is a little more complicated than others and involves some setup work. It's worth it though! A checksum is a method used to reduce a files validity into a single number. Adding up the values of the bytes which make up the file would be a simple checksum method. Doing more complex mathematics allows for more and more checking information to be included in a test. If you use a lie on the form: C=C:\COMMAND.COM[12345] then when FLU_SHOT+ first loads it will check the validity of the file against the number in the square brackets. If the checksum calculated does not match the number presented, you'll be advised with a triggering of FLUSHOT, which presents the correct checksum. When you first set up your FLUSHOT.DAT file, use a dummy number such as '12345' for each of the files you wish to checksum. Then, when you run FLUSHOT, you should copy down the "erroneous" checksum presented. Then, edit the FLUSHOT.DAT file and replace the dummy number with the actual checksum value you had copied down. Voila! If even one byte in the is changed, you'll be advised the next time you run FLU_SHOT+. But wait! There's more! Not available in stores! Sorry. I got carried away. Seriously, there is more. When a "checksummed" file is loaded by MS-DOS, it will, by default, be checksummed again. So, if you had a line such as: C=C:\usr\bin\WS.COM[12345] the venerable old WordStar program (still *my* editor of choice!) would be checksummed each time you went to edit a file. Of course, you might not want the overhead of that checksumming to take place each time you load a program. Therefore, a few switches have been added. The switches are place immediately after the ']' in the checksum line: C=C:\usr\bin\WS.COM[12345]<switch> These switches are: ,n - will only checksum the file only 'n' times. Only one digit allowed. 16 - - Only checksum this file when FLU_SHOT+ first loads. ',1' and '-' are equivalent. + - Only checksum this file when it is loaded and executed, not when FLU_SHOT+ first loads Therefore, if you wished to only check your WS.COM file when you first loaded the FLU_SHOT+ program, you'd specify a line as: C=C:\usr\bin\ws.com[12345],1 or C=C:\usr\bin\ws.com[12345]- If you wished to checksum your program called "MY_PROG.EXE" only when it was used, try: C=C:\path\MY_PROG.EXE[12345]+ Registering a TSR program ========================= Any unregistered TSR program which is run after FLU_SHOT+ will cause a trigger when they "go TSR". You can register a program so no trigger goes off by specifying it in a line such as: T=C:\usr\bin\tsr_s\sk.com which will keep FLU_SHOT+ from complaining about sk.com. Make sure to take a look at the '-T' option, specified in the next section. Restricted Access ================= Normally, when access to a file causes FLU_SHOT+ to trigger, the user is given the option of hitting a 'Y' to allow the access, or a 'G' to allow the access until program exit or a key is hit. However, in some cases, access to a file should *never* be allowed. If you end a line in your FLUSHOT.DAT file with an '!', then the trigger will indicate that this is a restricted access file, and the user will be asked to press a key to continue. In any case, trigger accesses resulting from a line with a '!' at the end will not be allowed to go forth. For example, if you never want anyone to be able to read an AUTOEXEC.BAT file on any of your disks, have a line of the form: R=*AUTOEXEC.BAT! in your FLUSHOT.DAT file. That's pretty easy! (Make sure, however, to take a look at the FSP command line arguments for the '--' switch.) 17 Protecting the FLUSHOT.DAT file =============================== Obviously, the weak link in the chain of the protection which FLU_SHOT+ offers you is the FLUSHOT.DAT file. You would think that you'd want to protect the FLUSHOT.DAT file from reads and writes as specified above. However this, too, leaves a gaping security hole: memory could be searched for it, and it could be located that way. A better alternative exists. In the distribution package for FLUSHOT+ exists a program called FLU_POKE.COM. This program allows you to specify the new name you wish to call the FLUSHOT.DAT file. Simply type: FLU_POKE <flushot_name> where <flushot_name> represents the full path filename of your copy of FLU_SHOT+. You'll be prompted for the name of the FLUSHOT.DAT file. Enter the name you've selected (remember to specify the disk and directory as part of the name). Voila! Nothing could be easier. Here's an example, assuming that you've already named your FLUSHOT.DAT to FRED.TXT, and it resides in the C:\DOC directory. Assume that FSP.COM is in the current directory and has been renamed to MYFILE.COM. Here's the command line: FLU_POKE MYFILE.COM File opened ok... Enter the FLUSHOT.DAT filename (full pathname): FRED.TXT Protection Recommendations ========================== Here's a sample FLUSHOT.DAT file, basically the same one included in the archive. Your actual checksums will differ, and you may want to modify what files and directories are protected. Obviously, your exact needs are different than mine, so consider this a generic FLUSHOT.DAT: P=*.bat P=*.sys P=*.exe P=*.com R=*AUTOEXEC.BAT R=*CONFIG.SYS E=?\dev\* C=C:\COMMAND.COM[12345]- C=C:\IBMBIO.COM[12345]- C=C:\IBMDOS.COM[12345]- 18 Allowing "dangerous" programs to run ==================================== In some cases, though, you'll still want the ability to let "trusted" programs to run -- even if they are potentially dangerous. A good example of this is the DOS FORMAT program: here is a program specifically designed to overwrite the data on your disk in such a way that it would be difficult, at best, to recover. Yet, the program is a necessary part of your day-to-day computer usage. Therefore, the 'X=' switch has been added in to allow a program such as FORMAT to run without interruption. THIS IS A POTENTIAL SECURITY HOLE. To prevent an 'X=' program from being corrupted, I suggest you also include any 'X=' program as both a 'C=' and a 'P=' program as well: any writes to the file would cause FLU_SHOT to trigger, and you wouldn't be able to run a modified program without first giving FLU_SHOT permission. Use 'X=' sparingly. I'm rather uncomfortable with it myself. Protecting Your Boot Track ========================== Some of the virus writers out there are getting pretty devious: they are creating viruses which will replace your "boot record" with something of their own creation which will first create a virus upon a system boot, then will run your actual boot program. The "boot program" is a small program at the beginning of your disk, telling the system what to do when you first turn the system on. What makes these types of viruses particularly dangerous is that they are run before FLU_SHOT+ can be run: by the time FLU_SHOT+ is running, you're already infected! Therefore, you might want to consider using the Boot Checksum option line in your FLUSHOT.DAT file. It takes the form of: B=<disk><checksum> where <disk> is a single character (no ':') indicating which disk drive you boot from, and checksum is the boot checksum. The boot checksum is checked each time you exit a program and when you first invoke FLU_SHOT+. First, create a bogus boot checksum entry, as in: B=C12345 then, run FLU_SHOT+. You'll be advised of what the actual boot checksum is, and you should edit that checksum into the "B=" line. That's it! You're now protected from some virus program somehow getting around the protections FLU_SHOT+ offers and modifying the boot record, and you'll be advised if something changed your boot record while you weren't looking. Never boot off a floppy if you can avoid it, though: that's how a lot of viruses spread! 19 Invoking FLU_SHOT+ Running FLUSHOT+ ================ For extra protection, after you've run FLU_POKE, you should rename the FLU_SHOT+ program is something unique and meaningful to you, but not a worm. Assuming you didn't rename it, however, you could invoke the program simply by typing: FSP when at the prompt. That's all there is to it. When you're satisfied, you can add it to your AUTOEXEC.BAT file, after all of your trusted programs have run. But there are some options you should know about: Checksumming the in-memory table ================================ Since the wily worm may well be able to thwart some of the efforts of FLU_SHOT+ by playing nasty games with the in-memory copy of the FLUSHOT.DAT file, FLU_SHOT+ will also check this table against a checksum it generates on a regular basis. If the table gets corrupted, you'll be advised of it. This table is checked with each call to DOS, so the table must be in good shape before any disk I/O is done. 20 Intercepting Direct Disk Writes Through INT13 and INT40 ======================================================= The default operation of FLU_SHOT+ is to intercept and examine every call to the direct disk routines. You can *disable* this by including the '-F' switch on your command line: FSP -F This is not recommended, but exists primarily for developers who can't use the constant triggering one of their programs may cause. What about INT26 ================ Similarly, the same exists for the direct writes which normally are only made by DOS through interrupt 26. Again, I do not recommend you disable the checking, but if you desire to do so, use the '-D' switch. Turning off the header message ============================== If you've no desire to see the rather lengthy welcome message, displayed when you first use FLU_SHOT+, use the '-h' switch. Disabling Triggering on Open with Write Access ============================================== Files which are opened with write access allowed are often not ever written to. For example, a COPY A.COM B.COM will open *both* files for write access, although DOS will not actually write to the A.COM file. Programmer laziness is the most likely excuse, and I'm as guilty of it as anyone else. However, this can cause some false alarms, which can alarm you! If you specify the '-W' switch on your command line, you won't have this particular alert come up. Since the actual write operation to this file is also protected by FLU_SHOT+, there is no real danger with using the '-W' option -- except that a "protected" file could be created anew without you being triggered. That's not too big a deal. Future versions of FLU_SHOT+ will most probably have the '-W' option as the default operation. Changing the Trigger Window Attributes ====================================== Certain displays, particularly monochrome displays which try to emulate color displays, have a problem with the default selection of attributed in the trigger window of FLU_SHOT+. If you use the '-Axx:yy' switch, you can modify these attributes. The xx:yy represent the hex values (as selected from the table below) for the interior and the perimeter of the trigger window. The 'xx' represents the interior attribute, the 'yy', the 21 perimeter. If you use the '-A' switch, you *must* select both of these values - failure to do so may give a rather strange display. What follows is a table of color and characteristics associated with the attribute byte. A byte has eight bits. Counting from the leftmost bit, the first bit of the attribute byte, if set, will cause the character to blink, regardless of other settings. The next three bits represent the background color for a given character position. The next bit indicates whether a character should have high intensity turned on. Finally, the last three bits represent the color of the character itself. To create the color of your choice, simply combine the bits, then calculate what they are in hexadecimal. If you're not sure of how to create a hexadecimal representation of a binary number, have no fear: that information follows, too. Bkgrnd Frgrnd B CLR I CLR [] [][][] [] [][][] Brightness----^ | | | | | | | Background-------+-+-+ | | | | Intensity---------------+ | | | Foreground-----------------+-+-+ Value in hex Bit Pattern Value Color if B or I set ==================================================== 0 0 0 0 Black 8 0 0 1 1 Blue 9 0 1 0 2 Green a 0 1 1 3 Cyan b 1 0 0 4 Red c 1 0 1 5 Magenta d 1 1 0 6 Yellow e 1 1 1 7 White f For example, to create an attribute byte that is high intensity, blinking yellow characters on a green background, the attribute byte would be: Bkgrnd Frgrnd B CLR I CLR 1 0 1 0 1 1 1 0 \--------/ \-------/ | | A E Attribute char: AE IMPORTANT: If the value is less than 10 (hex), you *must* include a leading zero or strange things will happen to the selected value. 22 Allowing Trusted TSR's to Work ============================== Normally, you'd load all of your trusted TSR's before FLUSHOT+ is loaded from within your AUTOEXEC.BAT file. However, you might want to use SideKick once in a while, removing it from memory as you desire. This could cause some problems, since SideKick, and programs like it, take over certain interrupts, and FLU_SHOT+ could get confused about whether this is a valid call or a call that shouldn't be allowed. Normally, FLU_SHOT+ will trigger on these calls, which is safer, but can be annoying. If you use the special '-T' switch upon program invocation, then calls which trusted TSR's (those specified with the 'T=' command in your FLUSHOT.DAT file) make will be allowed. Understand, please, that this basically means that calls made by a Trojan while a trusted TSR is loaded may not be caught. Please, use this switch with caution! Disabling FLU_SHOT+ =================== There may be times when you're about to do some work which you know will trigger FLU_SHOT+. And you might not want to be bothered with all of the triggering, the pop-up windows and your need to respond to each trigger. If you look in the upper right hand corner of your screen, you'll see a '+' sign. This indicates that FLU_SHOT+ is monitoring and attempting to protect your system. Depress the ALT key three times. Notice that the '+' sign' turned into a '-'? Well, FLU_SHOT+ is now disabled, and will not trigger on any event. If you depress the ALT key three more times, you'll see the '-' turn back into a '+' -- each time you depress the ALT key three times, FLU_SHOT+ will toggle between being enabled and disabled. Disabling the Disabling of FLU_SHOT+ ==================================== Yes, I know about the poor grammar used in the heading, but I couldn't think of a better way of expressing it. You can cause FLU_SHOT+ to ignore the "strike ALT three times" function discussed above. If you'd rather that the people using the machine FLU_SHOT is working on *not* be able to disable it, then enter the '--' switch on the command line, as in: FSP -- this is important when used in combination with the '!' restricted file access option you may have opted to use in your FLUSHOT.DAT file. 23 Disabling FLU_SHOT+ Toggle Display ================================== Alas, there are graphics applications which will be screwed up be the '-' or '+' in the upper right hand corner of your display. Therefore, if you depress the CTRL key three times, you'll be able to toggle the display capability of FLU_SHOT+. The default configuration of FLU_SHOT+ is to "come up" with display turned on. You can reverse this capability if you include the '-G' (for graphics) switch on your command line when you run FLU_SHOT+. When you toggle this function, the '-' or the '+' won't appear or disappear immediately. Simply that the repainting of them will no longer take place. Defining Your Own "Special Keys" ================================ If you would like to, you can define your own "special keys" (as in the default Alt and Ctrl keys in a similar way as you define your attributes above. Use the '-Kxx:yy' option, which takes the hexadecimal scan code value for the replacement Alt key as the first argument (the 'xx') and the hexadecimal scan code value for the replacement Ctrl key value. If you're not sure of what your scan codes are, you should look them up in your BIOS tech ref manual -- or there are a multitude of programs which will print out the scan code for a given key. Most of these programs are available on BBS's throughout the world, including the Software Concepts Design, RamNet BBS at (607)-326-4425. Due to extreme programmer fatigue, the "Welcome" message you see when you first run FLU_SHOT+ with the '-K' option will not change to reflect your selection. Maybe in the next version. And, of course, it depends upon how much you, the end-user want such an option. IMPORTANT: If the value is less than 10 (hex), you *must* include a leading zero or strange things will happen to the selected value. Forcing FLU_SHOT+ to only use the BIOS ====================================== Certain machines are not totally compatible with the IBM BIOS, which is the BIOS for which FLU_SHOT+ was written. Because FLU_SHOT has to be able to deal with the hardware in a pretty direct manner in order to "pop-up" a screen, these machines were not able to use FLU_SHOT. If you specify the '-B' switch in your command line when you first run FLU_SHOT+, then only the BIOS will be used for screen output. This is *drastically* slower than direct screen memory writes (the method used unless you specify to use the BIOS), but at least it works. However, the "hit ALT and/or CTRL three times" options may not work in these machines - only your experimentation will tell. 24 Putting FLU_SHOT+ to Sleep When Its First Run ============================================== One of the idiosyncrasies of DOS is how a batch file is processed. Basically, DOS opens the batch file, reads the next command, closes the batch file, executes the command, and then starts over again until the batch file is exhausted of commands. This would, normally, not be a problem, but can become when you opt to place the FLU_SHOT command line in your AUTOEXEC.BAT file *and* you've opted to Read Protect (with the 'R=' option) the AUTOEXEC file itself: you'll be advised that some program is reading this protected file. Not a big deal, really, but certainly a hassle when you fist boot up your system. Therefore, protections within FLU_SHOT are not turned on a certain amount of time. The default is set to ten seconds, or until you enter a key. You can modify the default "sleep" time by entering a '-Sn' option on the command line, where 'n' represents the number of eighteenths of a second (1/18) you wish to have FLU_SHOT+ sleep before becoming active. Since you will most likely have FLU_SHOT+ as one of the final commands in your AUTOEXEC.BAT, you probably won't have to modify this parameter, but the capability exists, nonetheless. 25 Interpreting a FLU_SHOT+ Trigger ================================ So, you've run FLU_SHOT+, and you're at your C> prompt. Great! Now stick a blank disk which you don't care about into your A: drive and try to format it. Surprise! FLU_SHOT+ caught the attempt! You have three choices now: typing 'Y' allows the operation to continue, but the next one will be caught as well. Typing a 'G' (for Go!) allows the operation to continue, disabling FLU_SHOT+ until an exit from the program is made. When FLU_SHOT+ is in the 'G' state, a 'G' will appear in the upper right hand corner of your screen. Any other key will cause a failure of the operation to occur. When you've got FLU_SHOT+ running and you get signaled that there is a problem, you should think about what might have caused the problem. Some programs, like FORMAT, or the Norton Utilities or PC-Tools, or DREP have very good reasons for doing direct reads and writes to your hard disk. However, a public domain checkbook accounting program doesn't. You'll have to be the judge of what are legitimate operations and which are questionable. There is no reason to write to IBMBIO or IBMDOS, right? Wrong! When you format a disk with the '/S' option, those files are created on the target diskette. The act of creating, opening up and writing those files will trigger FLU_SHOT+ as part of its expected operation. There are many other legitimate operations which may cause FLU_SHOT+ to trigger. So will copying a COM or EXE file if you have those protected with a 'P=' command. FLU_SHOT+ is not particularly intelligent about what is allowed and what isn't. That's where you, the pilot, get to decide. Here's a fuller listing of the messages which you might see when you're using FLU_SHOT+: Checking ===><filename> This message is displayed as FLU_SHOT+ checks the checksum on all of the "C=" files when you first invoke FLU_SHOT+. The files must be read in from disk, their checksum calculated and then compared against the value you claim the checksum should equal. 26 If the checksum does *not* equal what you claim it should (which means that the file may have been written to and might therefore be suspect), a window will pop up in the middle of your screen: +===============================================================+ | Bad Checksum on <filename> | | Actual Checksum is: <checksum> | |Press "Y" to allow, "G" to go till exit, any other key to exit.| +===============================================================+ This message simultaneously advises you there is a problem with the checksums not matching, shows you what the checksum should be and then awaits your response. Except for the initial run of FLU_SHOT+, if you type a 'Y' or a 'G', then the program will load and execute. Typing any other key will cause the program to abort and for you to be returned to the C> prompt. When FLU_SHOT+ is in the 'G' state, a 'G' will appear in the upper right hand corner of your screen. If this is the initial run of FLU_SHOT+, however, you'll be advised of the program's actual checksum, but FLU_SHOT+ will continue to run, checking all remaining "C=" files in the FLUSHOT.DAT file. If you're running a program and you see a screen like: +===============================================================+ | ? WARNING! TSR Request from an unregistered program! | |Number of paragraphs of memory requested (in decimal) are:<cnt>| | (Press any key to continue) | +===============================================================+ you're being advised that a program is about to go TSR. If this is a program you trust (such as SideKick, of KBHIT, or a host of other TSR programs you've grown to know and love), then you should considering installing a "T=" line in the FLUSHOT.DAT file so that future runs of this program will not trigger FLU_SHOT+. However, if you get this message when running a program you don't think has any need to go TSR (such as the proverbial checkbook balancing program), you should be a little suspicious. Having a TSR program is not, in of and of itself, something to be suspicious of. But having one you don't expect --- well, that's a different story. Most TSR's "hook into" an interrupt vector before they go TSR. These hooks might intercept and process key strokes ("hotkeys"), or they might hook and intercept direct disk writes themselves. In any event, FLU_SHOT+ (in this version!) doesn't have the smarts to do more than advise you of the TSR'ing of the program. If you're truly suspicious, reboot your machine immediately! 27 If a program attempts to write directly to the interrupts which are reserved for disk writes, FLU_SHOT+ will also be triggered and you'll see something like: +===============================================================+ |====>Direct Disk Write attempt by program other than DOS! <====| | Interrupt xx=> Drive: x Head: y Track: zzzzz Sector: zzzzz | | By: <program> | |Press "Y" to allow, "G" to go till exit, any other key to fail.| +===============================================================+ where the <xx> represents either a 13 or 40 (indicating a direct BIOS write to the disk) or a 26 (indicating a direct DOS write). Again, pressing a 'Y' or a 'G' allows the operation to continue, pressing any other key will cause the operation to return a failed status to DOS, and the operation will not take place. When FLU_SHOT+ is in the 'G' state, a 'G' will appear in the upper right hand corner of your screen. FLU_SHOT+ will attempt to let you know what program is actually attempting the write as well: this is not always reliable, though, so don't count on it as more than a hint. Additionally, for the folks interested in the real techno-babble, FLU_SHOT+ will also let you know what drive, head, track and sector is the target of the supposed "illegal" access. If an attempt is made to format your disk, which may be a legitimate operation made by the DOS FORMAT program, you'll see a message such as: +===============================================================+ | ====>Disk being formatted! Are You Sure?<==== | | Interrupt xx=> Drive: x Head: y Track: zzzzz Sector: zzzzz | | By: <program> | |Press "Y" to allow, "G" to go till exit, any other key to fail.| +===============================================================+ which follows similarly to the direct disk write operations. You should question whether the format operation is appropriate at the time and take whatever action you think is best. If one of your protected files is about to be written to, you'll see a message like: +===============================================================+ |Write access being attempted on: | | <filename> | | By: <program> | |Press "Y" to allow, "G" to go till exit, any other key to fail.| +===============================================================+ where <filename> represents the file you're trying to protect from these write operations. Your red flag should fly, and you should question why the program currently running should cause such an operation. 28 You may also see the same type of message when one of your "Read- Protected" files is being accessed: +===============================================================+ |Read Access being attempted on: | | <filename> | | By: <program> | |Press "Y" to allow, "G" to go till exit, any other key to fail.| +===============================================================+ Again, the same red flag should fly, but it doesn't mean that you're infected with some nasty virus program! It could be something harmless or intended. You'll have to be the judge. +===============================================================+ |Open File with Write access being attempted on: | | <filename> | | By: <program> | |Press "Y" to allow, "G" to go till exit, any other key to fail.| +===============================================================+ If you see the above message: Don't Panic! When a program opens a file, it may open the file for different types of access. One access method prohibits writing to the file. Another allows you to write to the file. However, lazy programmers (myself included in this category from time to time) will often open a file for read *and* write access, even though they have no intention of ever doing a write into the file. FLU_SHOT+ isn't smart enough to be able to figure out what a program *might* do in the future, so it will alert you to an attempt to open the indicated protected file with write access allowed. Again, you'll have to consider whether the program opening the file is a "trusted" program or not and you'll have to then decide what action to take. +===============================================================+ |Handle Write Access being attempted on: | | <filename> | | By: <program> | |Press "Y" to allow, "G" to go till exit, any other key to fail.| +===============================================================+ If you see this message, it means that some program is trying to write to a protected file through an access method known as "handle access". This should normally never happen, with the caveats raised above in the "Open With Write Access" section. 29 There are three separate messages you'll see if a program attempts to rename a protected file (you'll only see one of these messages at a time, though): +===============================================================+ |FCB Rename being attempted on source file: | |FCB Rename being attempted on target file: | |Handle Rename being attempted on: | | <filename> | | By: <program> | |Press "Y" to allow, "G" to go till exit, any other key to fail.| +===============================================================+ This indicates what type of operation is attempting to rename a protected file. FCB's are a relic of the older CP/M days, and "handles" are a newer concept, a little more modern. In any event, this tells you that a file is being renamed. It is possible that a trojan or virus writer will attempt to rename an existing protected file to some other name, then rename a trojaned or virused program in its stead. FLU_SHOT will alert you to this action: again, though, you'll have to decide what to do about it. +===============================================================+ |Delete being attempted on: | | <filename> | | By: <program> | |Press "Y" to allow, "G" to go till exit, any other key to fail.| +===============================================================+ Pretty much self-evident as to what's happening here, there are very few reasons why one of the files you've opted to protect should be deleted. 30 How Good is FLUSHOT+, Really? FLU_SHOT+ is a pretty handy piece of code. But, it can't absolutely protect you from a worm. No software can do that. There are ways around FLU_SHOT+. I'm of two minds about discussing them, since the worms out there are reading this, too. So I'll only discuss them in passing. And I'll tell you what I use here to protect myself from worms. First, though, a little story to tell you what it's like here, and how I protect myself from getting wormed. The RamNet Bulletin Board System site I run is open access. No need to register, or to leave your phone number or address, although a note to that effect is always appreciated. As mentioned above, I dare the worm to try to affect the disk of somebody who can fight back. A couple of of worms have tried and I have a nice collection of Trojans and viruses. Obviously, I run FLU_SHOT+ on my board, along with checking incoming files with CHK4BOMB. My procedure for testing out newly uploaded code involves me doing a backup, installing all sorts of software to monitor what is going on, and doing a checksum on all files on the disk. I then try out all of the code I get, primarily to determine if the code is of high enough quality to be posted. After testing out all of the weeks uploads, I run the checksum program again to determine of any of my files might have been modified by a worm's virus program. Recently, what looked like a decent little directory lister was posted to the board. For some reason I've yet to fathom, directory aid programs seem to be the ones which have the highest percentage of Trojans attached to them. This directory aid program listed my directories in a wonderful tree structure, using different colors for different types of files. Nice program. When it exited, however, it went out and looked for a directory with the word "FLU" in it. Once it found a directory with a match in it, it proceeded to try to erase all of the files in that directory. An assault! No big deal. That's what backups are for. But it brings up an interesting point: I was attacked by a clever worm, and it erased a bunch of files which were pretty valuable. All of the protection I had would have been for naught if I didn't use the first line of defense from these worms: full and adequate backup. I've spent three years of my life developing one particular software package. Imagine what would have happened if that had been erased by a worm! Fortunately, I make backups at least once a day, and usually more frequently than that. You should, too. Now, I quarantine that machine as well. I spent a couple of dollars and bought a bunch of bright red floppy disks. The basic rule around here is that Red Disks are the only disks that go into the BBS machine, and the Red Disks go into no other machine. 31 You see, I *know* that there is some worm out there who is gonna find some way to infect my system. No matter what software protection I use, there *is* a way around it. You needn't be concerned though -- you're making backups on a regular basis, right? And, you aren't asking for trouble. I am, I expect to find it, and it is sort of amusing to see what the worms out there are wasting their efforts on. At this point, Trojans and Viruses are becoming a hobby with me: watching what the worms try to do, figuring out a way to defend against it, and then updating the FLU_SHOT series. However, there is a possibility that the FLU_SHOT series (as well as other protection programs which are just as valuable) are causing an escalation of the terms of this war. The worms out there are sick individuals. They must enjoy causing the damage they do. But they haven't the guts to stand up and actually do something in person. They prefer to hide behind a mist of anonymity. But you have the ultimate defense! No, not the FLU_SHOT+ program. FULL AND ADEQUATE BACKUPS! There are a variety of very good backup programs which can save you more work than you can imagine. I use the FASTBACK+ program, which is a great little program. I backup 30Megs once in a while, and do an incremental backup on a very frequent basis. There are a variety of very good commercial, public domain, and shareware backup programs out there. Use them! Because, no matter what software protection you use, somebody will find a way around it once day. But they can't find a way around your backups. And, if you (and everyone else) do regular backups, you'll remove the only joy in life these worms have. They'll kill themselves, hopefully, and an entire subspecies will be wiped out -- and you'll be partially responsible! My advance thanks for helping to exterminate these little slimebuckets. But that brings me to something else. 32 Reward Offered Somebody out there knows who the worms are. Even they must have someone who is a friend. True, I can't think of any reason someone would befriend a worm. But somebody who doesn't know better has. Well, I'm offering a reward for the capture and conviction of these worms. Enough already with software protection schemes, hardware protection schemes, or any protection at all. It shouldn't be required, dammit! Here's the deal: In this archive is a form called REWARD.FRM. If you're a software or hardware manufacturer, or you have some software or hardware you don't need, consider filling out that form, and donating it to a worthy cause. I don't know what the legal and tax ramifications of that donation would be. I'm not a lawyer and we can cross that bridge when we get to it. Anyway, if you know one of these worms, turn them in! Call me up, send me a letter, a telegram, or leave a message for me on my BBS. Indicate who you *know* is worming about. I'll keep your name confidential. It is surprisingly easy to get the authorities in on this -- they're as concerned about what is happening to our community as we are. I'll presume that they'll end up putting a data tap on the phone line of the accused worm. Then, when he next uploads a Trojan or a virus to a BBS, he'll get nailed. The authorities are pretty good about this stuff: they'll not tap a phone or take any action whatsoever without adequate proof. Will your dropping a dime on this worm be adequate proof? I don't know. Again, a bridge to cross when we approach it. However, assuming that this slimeball gets nailed, you'll get all of the software and hardware which other people have donated. And the satisfaction of knowing that you've done a Good Thing, that you've helped an industry and community continue to grow. This *is* your community, and the vast majority of people in it are good people who shouldn't have to fear from your friend. Your friend is not really a friend: he uses you to justify his own existence. When someone uses you like that, they're not a friend, they're a leach. And you've probably got better things to do then let somebody use you like that. Most importantly, the worm out there won't know if one of his friends has already turned him in. So he won't know if his phone is tapped. If *I* were a worm, and considering what kind of friends I would have, I'd be sure that somebody dropped a dime on me. And therefore an intelligent worm (perhaps I'm giving the worm too much credit?) must presume that their line is tapped and 33 that they're gonna go to jail if they continue what they're doing. So just stop, you miserable little lowlife, huh? You're going to be arrested. You're going to have to put up with indignities which even you don't deserve! Your equipment will be confiscated. You'll never get a job in the industry. You're going to go to jail. All because one of your friend's actually has a conscience and knows what is right and what is wrong. And what you're doing is wrong. So, let me get back to the kind of programming I enjoy -- productive programming. And turn your programming to useful, interesting, and productive programming. You have the talent to do something useful and good with your life. What you're doing is hurting the industry and hurting the community which would welcome someone with your talents with open arms. And the satisfaction of helping far surpasses the satisfaction you must get from hurting innocent people. So just stop. Sincerely, Ross M. Greenberg 34 APPENDIX A: Common Questions and Their Answers: Q: Why does FLU_SHOT+ not work with programs that use graphics capabilities, such as Microsoft EXCEL? A: FLU_SHOT+ is a TSR program, and uses up memory on your computer even when there is no suspicious action taking place. When such an action occurs, the current screen must be saved to bring up the trigger window. In graphics mode, this requires a great deal of memory to be set aside, and so we considered it not worth the loss of memory Q: So, then, what can I do if I use such graphics programs? A: Try using the '-B' switch. You might lose a portion of your screen, but you'll be able to see what is causing the trigger to occur. Q: Certain programs lock up when FLU_SHOT+ triggers -- I have to reboot the system. What can I do? A: Try resetting the Action Keys (with the -Kxx:yy option). Chances are that your program is taking over the keyboard and not passing keys over to FLU_SHOT+. You'll have to experiment around with keys until you find a set that works. Q: Certain programs, like WORDPERFECT, use temporary work files, and then delete them with a call that triggers FLU_SHOT+. What can I do? A: Try excluding the class of files causing the trigger with the 'E=' option in your FLUSHOT.DAT file. Look for the pattern of the target filenames in the trigger window, and then install a line into FLUSHOT.DAT that corresponds to it. Or, you could exclude that particular directory if you wish. Q: Every time I run a program like "PRINT", I get a lot of Direct Disk Access messages from FLU_SHOT+. Does this mean that PRINT (for example) is infected with a virus? A: Not at all! PRINT is a TSR, which means that a portion of it stays around after you get back your C:> prompt. Part of that TSR takes over the Direct Disk Access Interrupts. Therefore, whenever even a legitimate program makes a call to do a legitimate disk operation, it appears to come from some program other than the DOS operating system. Try putting your PRINT (or other trusted TSR) command before the call to FLU_SHOT+ in your AUTOEXEC.BAT file. This should solve the problem. 35 Q: Will FLU_SHOT+ tell me if I have a virus on my disk and will it remove a virus if found? A: Nope. FLU_SHOT+ will check that files are what they appear to be when you run them, if you wish. And, it will interrupt the type of suspicious activity associated with a virus attack. At that point, you have to consider whether or not the program you're running is a virus or not, and take appropriate action if it is. Q: What kind of appropriate action? A: First thing to do would be to load a new copy of that program from your original distribution disk. Try using the program again. If the trigger window pops up, then chances are the program is violating one of the rules in your FLUSHOT.DAT file, but isn't a virus. Change your FLUSHOT.DAT to reflect whatever exceptions are needed to cause this program to no longer trigger. Q: What precautions should I take when reloading a program from my original distribution disks? A: You should power off your computer for about ten seconds. Reboot with a clean, write-protected copy (stick a piece of black tape over the write enable notch on the disk) in your A: drive. Then, do a "SYS" onto your hard disk to play it safe (see the DOS manuals for an explanation of what SYS does and how to use it), then reinstall your software. Q: I see a lot of copies of FLU_SHOT+ on the Bulletin Board Systems I use. Are they the same as this version? A: You'll have to check the version number to make sure -- but there's no guarantee that the version you see out on a BBS is going to be a clean copy of FLU_SHOT+ (unless you get it from one of the BBS's the author uploaded it to himself). The commercial releases have an installation program to aid you your installing FLU_SHOT+ and have a printed manual. Q: May I distribute this copy of the program onto BBS systems? A: You may only distribute the .ARC file on the Distribution Disk to BBS systems. Without any changes. If you distribute any other files from that disk, you will be in violation of copyright law -- and that's a federal offense! Q: If I get a virus, what should I do with the infected program? A: If you like, make a copy of the infected program and send it to us so we can examine it and determine, if possible, who might have released it and have them prosecuted. Otherwise, simply delete the infected program - a deleted virus can hurt no one. 36 Q: I'm interested in seeing what a virus is. Can you send me one? A: Sorry, we can't do that. Aside from the ethics of releasing a virus to an unknown person (even if a customer!), there are now some laws on the books making distribution of a virus a federal offense. Q: I ran out of space in my FLUSHOT.DAT file. Can I expand it out at all? A: Nope. It's of a fixed size in this release of FLU_SHOT+. There's a big brother of FLU_SHOT+, called FLU_SHOT++, which provides for an unlimited size for your Protections File. Send in the card for more information on FLU_SHOT++ and the additional protections it affords. Q: Will FLU_SHOT+ stop every virus out there? A: No. No software product can stop every virus attack, since there are a variety of ways a virus can attack your system and get around FLU_SHOT+'s protection mechanisms. However, no virus can infect a program and not change the checksum of the program. Therefore, use the C= option in your FLUSHOT.DAT Protections File on all the programs you run. That way, you'll know if the program you're running has become infected since the last time you ran it. Q: ???? A: 42 37 APPENDIX B: How Does A Virus Work? A computer virus is actually a very simple program to write. First, a little bit of terminology can help understand what they are: A computer virus has a number of different parts. First, some viruses (some people consider the plural of 'virus' to be 'virii' -- I don't) have what is called a 'pre-trigger'. If the pre- trigger does not go off, then the infected program will work normally, as if not infected. What makes a pre-trigger go off? Almost anything the virus writer wants. It can be made to go off when the disk is more than a certain amount full, or when more than a certain amount of memory is in use by your programs. Or, perhaps, when a certain date comes or has past. Or, if a certain program exists on your hard disk. Fancifully speaking, it could be set to go off on the correct phase of the moon. Once the pre-trigger goes off (not many viruses have them, by the way), the next phase, the 'replication aspect' phase, gets initiated. Viruses seem to come in two flavors: the transient virus, which is only active when you're running your code, and the Terminate and Stay Resident kind, which stay active from the time initiated until you reboot your computer. There's a third kind, called a 'boot sector' virus, but that'll be discussed below. When you invoke a program, infected or not, your computer will read the image of the program from the disk into the computers memory, do a little bit of futzing with the program (if it's an program, letting the program tell it what to do from that point onwards. The computer's operating system, in this case MS-DOS, is really stupid: it gives total control to the running program from that moment until the program exits and you get back to your command line prompt. When you invoke an infected program, it is run just as any other program. The virus portion of that program will typically be run first. After passing the pre-trigger (if any), the replication aspect will consider what types of files to infect. For the standard transient virus, this usually means that a given directory will have one or more of its .COM or .EXE files infected. Some viruses will infect only one program each time they are run, some will infect many. It's up to the virus writer. Each virus has some characteristic about it which is unique, and often the virus writer will examine the target .COM or .EXE file for this characteristic to see if the target program is already infected. If it is, then the program will be passed over and the next one examined and potentially infected. Since the computer simply passes control onto the program once it is loaded into memory, and then basically forgets about it, if the first few instructions of the program can be changed to cause the computer to execute some new instructions, it will blindly do 38 so. And that's what a virus does. It takes the first few instructions of the program, saves them someplace, and replaces those instructions with a call to jump to the virus code. When the virus infected program executes later, it will first run the virus code, then restore the original code (unless the virus "goes off", discussed below), and finally will jump to the beginning of the reconstructed program. The infected program executes as if nothing had happened at all. So, when a virus goes to infect another program, it must add code to it. And, must replace at least a few instructions, at least temporarily, with some of its own. Typically, a virus will add to the end of a program, although not all viruses work that way. This is how almost all transient viruses work. Another, more sophisticated virus, is called the "TSR virus". This infects a program similarly to the transient virus, but its "action" involves leaving a little piece of itself behind (those in the anti-virus field seem to always call that small part left behind the "worm trail", or the "slime"). This piece becomes an active, and permanent, part of your computers operating system. Typically, it will look for instructions your computer sends in response to you entering a run command. When you do, it infects the program you've requested to run before it is actually executed, then executes it. Going back to the phases, the third phase is called the "trigger aspect". Like the pre-trigger, it depends on how devious the virus writer is when he or she creates the trigger, and can go off on just about anything. When it goes off, the final (and most dangerous) phase of the virus is reached: the "Trojan aspect". This is the part that deletes files, trashes your hard disk, or otherwise makes your life miserable. And, that's all there is a virus. An ingenious little piece of code. Written by a warped person. Who could spend their time better if they spent it doing something constructive instead of destructive. We already know that, of course. When they mature a bit, hopefully they'll find that out. Before they've hurt anyone else. Oh! Almost forgot about Boot Sector Viruses. Here goes: When you turn your computer on, a small program is run before anything else. That's called the Boot Sector, and it loads up some of the important stuff you need to have on your computer in order for it work. Little things, like the operating system. Without the operating system (MS-DOS), your computer is an expensive paperweight. Without the Boot Sector, and the program thereon, you have an expensive paperweight with an inoperable 39 operating system on it. A Boot Sector Virus replaces the current boot program with itself, and sticks the original boot sector onto an unused portion of your disk. After the Boot Sector Virus has run, leaving behind a sleazy little worm trail of its own, it will execute the original boot program. You'll have an infected system even before an anti-virus program is run! When you access some other disk, the worm trail of the Boot Sector Virus will examine the boot sector of that disk. If not infected, it will infect it. Very simple. And the infected diskette waits for you to pass it on to one of your friends, who will then (by booting on that disk) infect their own drive. And so. The moral here: never boot up your system on anyone else's disk and you'll be a much happier person. 40