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A description of PC viruses and their symptoms - Part II Jerusalem (Israeli "Friday 13.") The Jerusalem virus is one of the oldest and most common viruses around. As a result there are numerous variants of it. It will infect both .EXE and .COM files, but the first version of the virus contained a bug, causing it to infect .EXE files over and over, until they became too large for the computer. Needless to say, this has been fixed in later releases, including one called "New Jerusalem". Infected files grow by 1808 bytes or so. The original Jerusalem virus would activate on every Friday the 13th, deleting programs run on that day. 30 minutes after an infected program is run, the virus will also cause a general slowdown of the computer and make a part of the screen scroll up two lines. This has been disabled in some variants of the virus, which makes them much harder to detect. The first variant of the virus (sURIV 3.00) produced the side-effects described above 30 seconds after an infected program was run. One variant, "Century" will become active on Jan 1. 2000. It will try to delete everything that can be deleted and then display the message Welcome to the 21st Century The programmer does not seem to have known that the 21st century does not start until a year later. The "Sunday" virus is another variant of the Jerusalem virus. Instead of activating on Friday the 13th, it will activate if the current day of the week is Sunday and display the message: Today is SunDay! Why do you work so hard? All work and no play make you a dull boy! Come on! Let's go out and have some fun! Apart from this the viruses are very similar. A second variant, Sunday-2 is also known, containing some minor changes. Other variants include Payday, Anarkia, PSQR, Mendoza, Puerto, Spanish, Westwood and A-204, which are only different in minor ways - different activation dates and other minor changes. Sometimes the changes only involve the reordering of a few instructions, perhaps to prevent the virus from being detected by some virus scanning program. Perhaps the most unusual variant is "Frere", which is reported to play "Frere Jacques" on Fridays, when it activates and "Groen Links", a Dutch variant, which plays a tune whose name translates to "Vote Green Left" ("Green Left" is a political party there). Jo-Jo This virus is a 1701 byte, memory resident .COM infector, which is basically a patched, non-encrypted variant of the Cascade virus. It is reported to have originated in Barcelona or Israel. It contains a check for the IBM copyright message at address F000:E008, just like Cascade. The virus contains two text strings: Welcome to the JOJO virus. Fuck the system (c) - 1990 Joker This virus is probably extinct, but it originated in Poland, and is 11000 bytes long. It will overwrite .EXE files, and is therefore easily detected. Infected programs will display silly messages when executed, like Water detect in Co-processor I'm hungry Insert HAMBUGER in drive A: Joker-01 This is also a large Polish virus - 29233 bytes long. It infects files in the same way as Vacsina - COM files are infected normally, but EXE files are converted to files with COM structure, by adding a small, 139 byte loader program to them. July 13th This virus is designed to activate on July 13th - which happened to fall on a Friday in 1990. It is a 1201 byte encrypted .EXE file infector, which has not been fully dissected yet. Kemerovo A primitive, 257 byte direct-action Russian virus, which only infects COM files. It has not been fully analysed yet. Kennedy A simple .COM infecting virus, probably from Denmark. When an infected file is run, it will infect a single .COM file in the current directory, adding 333 bytes to the end of the file. The virus activates on three dates - June 6th, November 18th and November 22nd. On those dates it will display the message: Kennedy er d¢d - længe leve "The Dead Kennedys" There have been reports that infection by this virus may cause FAT corruption, crosslinking of files and loss of clusters, but I have not been able to verify this. Another variant is also known - which is one of the shortest virus known - only 163 bytes long. This variant seems to do nothing but replicate. Like the original Kennedy virus, this variant, which is known as 'Tiny' has only been reported in Denmark. It is somewhat carelessly written - it does not close the files it opens, for example. Lehigh The Lehigh virus is rather unusual in that it only infects one program, COMMAND.COM. It does not increase the size of the program, because it overwrites the stack space. This virus is rather badly written - it can be defeated by simply making COMMAND.COM read-only. It is, however, very destructive. "Lehigh" contains an infection counter and when it has reached a specific number of infections it will trash the disk. This means that the virus never got a chance to spread much outside Lehigh University. Leprosy-B The name of the virus is derived from the following message found inside it. ATTENTION! Your computer has been afflicted with the incurable decay that is the fate wrought by Leprosy Strain B, a virus employing Cybernetic Mutation Technology(tm) and invented by PCM2 08/90. Infected programs will either display this message or Program too big to fit in memory This is a 666 byte overwriting virus, and disinfected programs must be deleted, as there is no way to remove the virus. Liberty Liberty originated in Indonesia. It is a resident .EXE and .COM infecting file, 2857 byte long. The virus code is placed at the end of the file, but the virus also overwrites the first 120 bytes with code and the following message: - M Y S T I C - COPYRIGHT (C) 1989-2000, by SsAsMsUsEsL A second variant, 2867 byte long is also known. The effects of the viruses are not fully known yet. Lozinsky This is a Russian, 1023 byte virus, which uses a simple encryption method. It only infects COM files, but has not been fully analyzed yet. MG MG stands for "Matematicheska Gimnazia", the name of the school in Varna in Bulgaria where the virus seems to have been written. This is a 500 byte .COM virus, which hides itself in the upper half of the interrupt table, causing programs like Netware to crash. MG-3 A 500 byte virus, which only infects .COM files. Awaiting analysis, but is probably related to the MG virus. MGTU A very simple, 273 byte Russian virus. It does not remain resident in memory, but will infect COM files when infected programs are run. MIX1 MIX1 was probably written in Israel, but it is derived from the Icelandic virus. There are two versions known, MIX1 and MIX1-B, practically identical. MIX1 displays a bouncing ball on the screen, and garbles all output going to the printer. It will also disable the NumLock key. MIX1 is larger than the Icelandic virus - 1618 or 1636 bytes, depending on the version. One unusual "feature" of MIX1 is that it will only infect files 8192 bytes long or larger. MLTI This 830 byte Russian virus contains the text: Eddie die somewhere in time! This programm was written in the city of Prostokwashino (C) 1990 RED DIAVOLYATA Hello! MLTI! The text is more understandable if one considers the similar text found in the "Eddie" virus written by Dark Avenger. Murphy The authors of this virus are known. They are Lubomir Mateev Mateev and Iani Lubomirov Brankov, both in Bulgaria. Murphy is a 1277 byte long, resident .COM and .EXE infecting virus. It is based on the Dark Avenger, but is not harmful. Inside it the following message can be found. Hello, I'm Murphy. Nice to meet you friend. I'm written since Nov/Dec. Copywrite (c)1989 by Lubo & Ian, Sofia, USM Laboratory. Another variant is also known. It is a bit longer, 1521 bytes, and the message is different: It's me - Murphy. Copywrite (c)1990 by Lubo & Ian, Sofia, USM Laboratory. Originally this virus was reported to jump into ROM basic every exact hour, possibly causing some clones to "hang", but the variant available to researchers in the West produces the "Bouncing Ball" effect every time INT 18 is executed. Nina This virus is only 256 bytes long, and derives its name from a the text string found at the end, which says simply "Nina". Like many other small viruses, this one is written in Bulgaria. Nomenklatura This virus appears to be of Bulgarian origin, as it contains a message in Bulgarian. This is a 1024 byte virus, which corrupts data on the disk, by modifying the FAT. Number of the Beast Like quite a few other viruses, this one was first reported in Bulgaria. It is 512 bytes long, but the length of infected files does not appear to increase. This is because the virus overwrites the first 512 bytes of the programs it infects with itself, and stores the original 512 bytes in the unused space after the end of the file. This is possible because DOS allocates file space in "clusters", which are usually 1024 or 2048 bytes long. In addition, if a program attempts to read from an infected file, while the virus is active in memory, the read operation will be intercepted and instead of finding the virus, the original code will be read instead. This means that the virus will be able to fool any checksum program, as well as any virus-scanning program if it is active in memory when the program is run. It does not matter how sophisticated the checksum algorithm is - if the virus is active in memory, no infected program can be detected. F-DRIVER will, however, stop the virus. At the end of the virus code, the string "666" appears - hence the name. Several new variants are also known in Bulgaria, where this string is missing, but they are functionally identical. Old Yankee There is some confusion regarding the various "Yankee Doodle" viruses. They all originated in Bulgaria and play the tune "Yankee Doodle", but their structure is different. This is the first one. It only infects .EXE files, increasing their length by 1961 bytes. When an infected program is run, the virus will search for a non-infected file. When it has been infected, the virus plays the melody, before the original program is executed. At the very end of the virus, the word "motherfucker" appears. Another version of the same virus is also known. The main difference is the length - the variant is only 1624 bytes long. Oropax This virus probably originated in W. Germany. It is not very harmful - when it activates it will just repeatedly play three melodies. The virus infects .COM files, other than COMMAND.COM. Infected files grow by 2756-2806 bytes, becoming a multiple of 51 bytes in length. This virus stays resident in memory, but it will not infect other programs when they are executed. Instead it will search for a file to infect when files are created or deleted, a subdirectory is created or the access mode of a file is changed. A few other functions may also trigger an infection. The virus uses a random number generator to decide when to become active, and if it does, it will start playing 5 minutes after an infected program is run. Parity This is a simple, 441 byte virus, which will infect one .COM file when an infected program is run. The virus may emulate a parity error, displaying PARITY CHECK 2 on the screen and halting the computer. Perfume A .COM infecting virus of German origin, that will sometimes ask the user a question and not run the infected file unless the answer is "4711", which is the name of a perfume. This virus will look for COMMAND.COM and infect it unless it is already infected. Infected files grow by 765 bytes. In the most common variant of the virus the questions have been overwritten with garbage. Phoenix This is a family of viruses from Bulgaria, containing 1226, Proud (1302), Evil (1701) and Phoenix (1704). They all infect .COM files, and use a complicated encryption method, which complicates detection somewhat. Piter This 529 byte Russian virus has not been analysed yet, but it infects only COM files, overwriting the beginning of the programs, and placing the original code at the end of the infected file. Plastique (AntiCAD) This is a family of viruses from Taiwan. They are members of the Jerusalem family, perhaps based on the Fu Manchu variant, but are long - one 2900, one 3012 and three 4096 byte variants. One of the 4096 byte variants is also known as "Invader". The 4096-byte variants also contain code for infecting the boot sector. The reason the viruses are also known as AntiCAD is that they are targeted against the AutoCAD program. When a program named ACAD.EXE is run or sometimes when Ctrl-Alt-Del is pressed, the viruses will activate, overwriting data on floppy disks and hard disks, as well as garbling the contents of the CMOS. Polimer The name of this virus is derived from a text message which infected programs may display when executed: A le'jobb kazetta a POLIMER kazetta ! Vegye ezt ! The virus is a simple, 512 byte .COM infector, which seems to be based partially on the Vienna virus. Pretoria (June 16th) Pretoria is a direct-action, .COM infecting virus from South Africa. It overwrites the first 879 bytes of infected files with itself, and stores the original 879 bytes at the end of the file. This makes it impossible to fully restore programs shorter than 879 bytes, as their original length is not stored anywhere. When an infected program is executed, the virus searches the entire current directory for .COM files to infect. As it uses a full-depth recursive directory search, this may take considerable time on an XT-class machine. On June 16th the execution of an infected file will cause all entries in the root directory to be changed to 'ZAPPED'. June 16th is the day when the Soweto riots first broke out. The virus uses a simple substitution encryption. Prudents This is a Direct-Action Spanish virus, 1205 bytes long, which infects .EXE files. It is probably written by the same author as the PSQR variant of the Jerusalem virus, as it checks if that virus is present, when it is run. This virus will overwrite the last 32 bytes of any file it infects, possibly destroying the victim. The virus activates on May 1st - May 4th of any year, interfering with disk writes. Saddam This virus is based on the Stupid virus, and is also from Israel. It is 919 byte long. The most obvious effect of the virus is to display: HEY SADDAM LEAVE QUEIT BEFORE I COME Shake Thake is a primitive 476 byte .COM infecting virus. It may infect the same program over and over, and infected programs may cause a reboot when executed. The name is derived from a string which is found inside the virus: Shake well before use ! This message is occasionally displayed when an infected program is run, followed by termination of the program. Slow This is a variant of the Jerusalem virus from Australia. Some reports indicate it may cause a slowdown of the system, but this has not been confirmed. The length is 1716 bytes, with extra 5 bytes added at the end of .COM files. The major difference between this virus and the standard Jerusalem virus is the use of a simple encryption in the Slow virus. A variant of Slow has been reported in California. This 2126 byte variant is known as "Scott's Valley". South African "Friday 13." This is one of the oldest viruses around, but it is very rare. In fact, it may even be extinct, apart from copies in the hands of virus researchers. It is a "direct action" virus, that will seek out one or more programs to infect, every time an infected program is run. It will only infect .COM files, which grow by 415-544 bytes, depending on the variant in question. The original virus is 419 bytes long. Like the Lehigh virus it can be stopped simply by making .COM files read-only. Most other viruses are not bothered by this, however. A version of this virus, called "Virus-B", where the destructive part has been disabled has been distributed for demonstration purposes. Stupid (Do-Nothing) The "Do-Nothing" or "Stupid" virus is not a well written one. In fact it is so badly written that in many cases it will simply cause the system to "hang", instead of properly infecting it. It seems that this virus was created by a lousy programmer, somewhere in Israel. It is not a serious threat. It will only work on machines with at least 640K of memory, because it always tries to hide itself at the same address, starting at 9000:0000. This virus infects .COM files, which grow by 583 bytes. The original infected program distributed by the author contained the string: (c)Stupid 1989 Virushmock! Subliminal As this wirus vas found close to where the Dyslexia was discovered and as the viruses are clearly related, they are believed to have been written by the same person - "Subliminal" probably just being an earlier version of the same virus. The Subliminal virus derives its name from its activity - it will continously display the text "LOVE, REMEMBER?" for a fraction of a second in a corner of the screen. Suomi This is an encrypted 1008 byte virus from Finland. It infects COMMAND.COM as soon as an infected program is run. The virus has not been fully analyzed yet. Superhack This is a 1077 byte virus, which infects .COM files in an ordinary way, but .EXE files are infected in a similar way, which prevents the virus from infecting .EXE files longer than 64K. The virus was written in Scotland and is known there as "Murphy". SVC This is the first Russian "stealth" virus. It is 1689 bytes long and infects COM and EXE files. It has not been analysed yet, but it contains the text string: (c) 1990 by SVC,Vers. 4.0 Sverdlov This is an encrypted, 1962 byte Russian virus, which was first discovered in Sverdlov. It is reported to display a moving banner across the screen, while playing the Russian national anthem. Afterwards drive C: is reported to be inaccessible and a low-level format is required to make it usable again. Svir This is an unremarkable 512 byte direct-action .EXE file virus. Its effects (if any) are not yet known. Sylvia This virus is a bit unusual, to say the least. It contains the following message: This program is infected by a HARMLESS Text-Virus V2.1 Send a FUNNY postcard to : Sylvia Verkade, Duinzoom 36b, 3235 CD Rockanje The Netherlands. You might get an ANTIVIRUS program..... It will display this message when an infected program is executed, but if the above text is tampered with, the following message, (which is stored in an encrypted form) will appear instead: FUCK YOU LAMER !!!! system halted...$ Some people have a weird sense of humor... As the text above indicates, the virus originated in the Netherlands. When an infected program is run, the virus will seek out up to 5 .COM files to infect. It will search drive C: and the current drive. The three system files, COMMAND.COM, IBMBIO.COM and IBMDOS.COM are not infected. The virus adds 1301 bytes to the beginning of the files it infects (and also 31 bytes to the end), but does no other damage. The girl mentioned above exists, but she says that she has no idea who the author is. It is very likely that he knows her, though. SysLock The SysLock virus infects .EXE and .COM files. It is a "Direct Action" virus that will search for files to infect when an infected program is executed. The virus will first modify the length of any program it infects, so it becomes a multiple of 16 bytes. Then the virus code, 3551 bytes is appended to the file. One unusual "feature" of this virus is that it will search the disk for the string "Microsoft" and change it into "MACROSOFT". The virus will not infect programs if the environment contains SYSLOCK=@. Four other variants of this virus are known. Two are called "Macho", since they both will change the string "Microsoft" into "MACHOSOFT". One is very close to the original virus, the other a bit different. The third variant, "Advent" will activate in December and then play "Oh, Tannenbaum". The last variant is 2232 bytes long and known as "Cookie", because it may display the message I want a COOKIE! Taiwan This virus seems to have appeared in Jan '90. It is a direct-action .COM infector, which activates on the 8th day of any month, overwriting the FAT and root directory of drives C: and D: Two variants are known, one is 708 bytes, but the other one is 743. Infected programs sometimes "hang", for some unknown reason. Tenbyte This is a 1554 byte long .COM and .EXE infecting virus that was by accident posted to the V-ALERT electronic mailing list, which is intended for urgent messages regarding virus infections. Just like the "Stupid" virus, it will only work on machines with at least 640K memory. It activates on September 1st, and stays active until December 31st. While active, it will corrupt all disk writes, deleting the first ten characters of any data written to the disk and add ten "garbage" characters at the end. This will cause destruction of data files, as well as preventing the compilation of any programs. Traceback The "Traceback" virus produces a screen display similar to that produced by the Cascade virus. There are of course differences, since the viruses are totally unrelated. Every file infected with "Traceback" contains the name of the file that infected it. This makes it possible to trace the path of the infection. Another difference is that it is possible to make the characters "jump" back up, by pressing keys on the keyboard, after all the characters on the screen have fallen down. There are two variants known of this virus, but the size is the only significant difference. The original virus is 3066 bytes long, but the variants are 2930 and 3031 bytes long. TUQ This is a simple, non-remarkable, 453 byte long .COM infecting virus, probably written in Germany. It has no effects other than replication. Turbo The name of the virus is derived from a text string contained inside it. The virus family contains two viruses, one 512 byte known as "Turbo Kukac", but the other as Turbo-448. Both viruses only infect COM files, and may cause program crashes. For example, COMMAND.COM will always crash if infected. Turku This is one of two viruses from Finland, the other being the "Suomi" virus. It will infect .COM and .EXE files. The length of the virus is either 1232 or 1472 bytes, depending on the file type. No interesting effects have been observed, other than occasional "repeats" of certain keys, when pressed. Vacsina and Yankee Doodle A programmer in Bulgaria has written a number of viruses - 50 different variants or so. Two of the variants, number 5 and 39 "escaped" to the West in 1989. One of the features of virus in this family is that they contain a version number system, similar to that used in the "Den Zuk" virus. If a virus in the family finds a file infected with an older version of itself, it will remove the infection and re-infect with the new version. A number of the variants play the tune "Yankee Doodle", but the viruses are not to be confused with the original "Yankee Doodle" virus, which is called "Old Yankee" by the F-FCHK program. This family can be divided into two groups, one consisting of versions numbered below 38, but the other one versions 38 and upwards. The first group is identified as "Vacsina" variants by F-FCHK, and the second one as "Yankee Doodle" variants. However, this division is based on differences in the internal structure of the viruses - several of the "Vacsina" viruses also play "Yankee Doodle". The "Vacsina" viruses seem to have been written originally to infect only .COM files. .EXE files are also infected, but that is done in two steps. First a short piece of code is added to the end of the file. Then a JMP command is added at the front of the file. This code seems to be based on the code used in FORMAT.COM and CHKDSK.COM in some versions of MS-DOS. When executed it will relocate the .EXE file. This makes the .EXE file structurally equivalent to a .COM file, so it can be infected as one. The second group (versions 38 and upwards) infects .EXE files in a "ordinary" way. Compared to most other viruses, these are fairly harmless. In the first versions a beep (BELL) is heard, every time a .COM-type file is successfully infected. As mentioned before, some of them play "Yankee Doodle", sometimes at 5 o'clock, but other variants play the tune when the computer is rebooted by pressing Ctrl-Alt-Del. The latest versions of the viruses contain several advanced features - including self-correcting Hamming code, disabling of debugging tools, and the ability to search for and remove the Ping-Pong and Cascade viruses. One related virus is also known, but it is shorter than any of the Yankee viruses, only 1049 bytes long. It seems to have been created by removing parts of the "Yankee" code. Vcomm An .EXE infecting virus that came from Poland. It is not very well written, but easy to study because the commented source code was included in the sample that arrived from there. When an infected program is run, it will infect one .EXE file in the current directory. Infected programs are first padded so their length becomes a multiple of 512 bytes. Then the virus adds 637 bytes to the end of the file. It will also install a resident part that will intercept any disk write and change it into a disk read. VFSI (Happy) This virus is believed to have been written by a student at the "Vish Finansovo-Stopanski Institut" in Bulgaria. It is a small, 437 byte, direct-action .COM-infecting virus. It can be stopped by making files read-only. When it activates, it may display the following messages. HELLO!!! HAPPY DAY and SUCCESS from virus 1.1 VFSI-Svistov Victor This is a 2442 byte .EXE and .COM virus from the USSR, at least according to the text found inside it: Victor V1.0 The Incredible High Performance Virus Enhanced versions available soon. This program was imported from USSR. Thanks to Ivan Little is yet known about its effects. Vienna This virus, also called DOS-62, UNESCO and 648 will only infect .COM files. When an infected file is run, the virus will search for an uninfected file and infect it. One out of eight files infected is destroyed, by overwriting the first few bytes with instructions that will cause a restart when the program is run. Infected files can be easily found because they contain an "impossible" value (62) in the "seconds" field of the time stamp. Unfortunately the source code to this virus has been published in a book: "Computer viruses: A High-Tech Disease", so it will probably become very common in the future. This version was modified slightly, in order to make it a little less harmful - it would only infect files in the current directory. The virus appends 648 bytes to the files it infects, but a 646 byte variant is also known. One variant of this virus, "Lisbon", has been found in Portugal. It has clearly been modified and reassembled - probably in order to fool signature-type anti-virus programs. This virus overwrites the beginning of the programs it destroys with "@AIDS". The GhostBalls virus is also closely related. Several other variants have been reported in Bulgaria. Some of them are so different that they have received a new name, "New Vienna". The Bulgarian variants are similar to the original virus, but the changes include: Different length - 435,367,354 and 348 bytes. Different damage function - formatting of hard disk. Critical error handler added. Other variants exist as well. One, named 'Violator' is 1055 bytes long, and it contains the following text strings: TransMogrified (TM) 1990 by RABID N`tnl Development Corp. Copyright (C) 1990 RABID ! Activation Date: 08/15/90 - Violator Strain B (Field Demo Test Version) *NOT TO BE DISTRIBUTED* The text seems to indicate the existence of another version, which has not yet been reported anywhere. Perhaps the most unusual variant is "Father Christmas" or "Choinka", which was discovered in Poland. It is 1881 bytes long, with most of the extra length devoted to a Christmas greeting. The Monxla or "Time" variant is 939 bytes long, and has different effects, depending on the exact time when it activates. Virdem This 1336-byte, direct action .COM-infecting virus was written in 1986, which makes it one of the oldest viruses in existence. It was written by R. Burger, the author of "Computer Viruses: A High-Tech Disease". It will not spread unless modified, because the virus makes it quite clear that the program has been infected. Virdem overwrites the first part of the program and appends the original code to the end of the file. At least two variants of this virus are known - one with all the text strings in German, but the other is an English language version. In addition, a modified 792 byte variant is also known, where all the text messages have been removed. Virus-90 The most interesting fact regarding this virus is that the author of it is known. He uploaded the virus to a number of BBS, saying that the source code was available for around $20. The virus is a simple .COM infector that adds 857 bytes to any file it infects. It will only infect files on drive A: and B: but it would be easy to "fix" that. An infected program will display the message "Infected!" when it is executed, but otherwise the virus does nothing at all. The virus was uploaded for educational purposes, according to the author, but has now been removed. A "new and improved" version, Virus-101 also exists. It infects .EXE files as well as .COM files, and is somewhat variable. Some attempts were made to make it difficult to disassemble or modify the virus, but this "protection" is easily defeated. The virus contains one unusual feature, it infects COMMAND.COM by overwriting it, in the same manner as the Lehigh virus does, so no change in length is visible. Unlike Virus-90, this virus was not made publically available. Voronezh This is a 1600 byte virus from Eastern Europe, which infects COM and EXE files. It overwrites the beginning of COM files, placing the original code in encrypted form at the end. EXE files are also infected in an unusual way - the original CS:PC is not changed, but the first 5 bytes of the program code are overwritten with a FAR CALL to the virus code. A related virus, 600 bytes long is also known, but it is only able to infect COM files. VP First reported in April '90, this virus is of the direct-action .COM infecting kind. It contains one unusual feature - at the beginning of the virus a variable number of NOP instructions (0-15 in number) are added. This is probably done in order to confuse "on-the-fly" virus scanners. The virus then appends 909 bytes containing the virus code. W13 This is a rather primitive .COM infecting virus. Two variants are known, the first one is 534 bytes long, but the second, with some bugs corrected, is only 507 bytes long. The variants are both of the "Direct Action" type and do nothing interesting. They are based on the Vienna virus, but mark infected files by setting the "month" field to 13, instead of setting the "seconds" field to 62. This virus originated in the Soviet Union. Whale This is a recent, rather remarkable virus. It is long, 9216 bytes and able to infect COM and EXE files. The increase in file size is not visible though, while the virus is active in memory, as it uses several advanced "stealth" methods. Other effects of the virus are not known, but one infected program displayed the following message when run: THE WHALE IN SEARCH OF THE 8 FISH I AM '~knzyvo}' IN HAMBURG addr error D9EB,02 Most of the virus is devoted to encryption and code which moves blocks of virus code around. This overhead results in a considerable slowdown of infected systems. Wisconsin Like the AntiPascal viruses, this one is targeted against Pascal programs. It even includes the string Death to Pascal in encrypted form. The virus is 825 byte long and only infects .COM files. XA1 The XA1 virus overwrites the first 1539 bytes of infected .COM files with itself and stores the original code at the end of the file. On April 1st, a part of the virus will activate - overwriting the boot sector with code that will cause the computer to "hang" on next boot-up. The virus will also activate on December 21st and stay active until the end of the year. It will then display a Christmas tree, and the text: Und er lebt doch noch: Der Tannenbaum! Frohe Weihnachten Zero Bug The "Zero Bug" will mark infected files in the same way as the Vienna virus, placing 62 in the "seconds" field of the timestamp of the .COM files it infects. Apart from this, the viruses are very dissimilar. This virus will search for COMMAND.COM, using the value of the COMSPEC environment variable to locate the file. Then it will remain resident, hook INT 60 and infect every .COM file run. After some time has passed, a "smiley" (ASCII 1) will appear on the screen and "eat" any zero it finds on the screen. The virus seems not too well written - containing some unreachable code, but it is unusual in some ways. When it infects a file, it will add 1536 bytes in front of the original code, just like the Agiplan virus. It also contains one "feature" that will probably be more used in the future - if the virus is active in memory and you look at a directory containing infected files, the virus will make the directory entries appear as they were before the infection. That is, you will not see any increase in file length. This method is also used by some of the latest viruses from Bulgaria. Zero Hunt (Minnow) This virus infects programs by overwriting them, but unlike most overwriting viruses it will generally not destroy the host program. This is because it will only overwrite unused areas within the program. The virus searches for a block of at least 416 zero bytes, and places itself there. As such programs are rare, this reduces the chances of the virus spreading.