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STVIRUS.TXT
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1989-08-31
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117 lines
VIRUSES (ST)
A companion document for the HOSPITAL
virus detection/prevention suite
Neil Forysth
Department of Computer Science
Heriot-Watt Univeristy
Hunters Close
79 Grassmarket
Edinburgh
neil@uk.ac.hw.cs
THE HOSPITAL PROGRAMS
It would be a lie to say that if you use the HOSPITAL programs
you will never suffer from a virus attack. The people(?) who
write viruses will eventually get these programs and try to
invent new ways of infection and avoiding detection. However,
using some combination of the programs is definately a good
precaution. They certainly do a great job against all the
viruses I've seen to date and should any smarter viruses come
along I will modify my programs accordingly.
Treat all formatted disks that you are given or buy with
suspicion. This includes commercially availiable packages. I
have seen a virus infected disk that came straight out of its
cling wrapped box. The software house was not being
irresponsible, they were the victim of a virus attack.
OTHER HELPFUL UTILITIES
AFMT by Neil Forsyth
In addition to the boot sector, some disk viruses use the
extra FAT sectors on a disk. There are usually six of these on
single sided disk and four on a double. They are never used on
the current double density disk systems.
The AFMT disk formatter reduces the size of the FAT to a
minimum leaving no free FAT sectors for a virus to hide in and
giving you more disk space.
DT (Disk Toolbox) by Neil Forsyth
This utility allows you to reversably change the executability
of a boot sector. If the boot sector does not contain a virus
and perhaps needs to be run for a program to work then it can
easily be changed back. The RAM loadable version of TOS from
Atari uses an executable boot sector to load as do a lot of
commercial games.
VKILLER by George Woodside
This is an excellent program for the bulk checking of disks
for possible viral infection. It has many features for
analysis and destruction of viruses. It can also tell you a
few things about any known viruses it finds.
FLU by George Woodside
This program demonstrates the symptoms of many of the joke
type viruses that George has come across.
LINK VIRUSES
There are some viruses that infect programs instead of disk
sectors. I have never seen one of these 'link viruses' but
have a pretty good idea how they might work and hope to create
programs to safeguard against them soon.
HARD DISK VIRUSES
Currently there does not seem to be any viruses that attack
hard disks but I'm sure that they will appear. The only advice
I can offer here is to back up your hard disk data regularly.
I do mean data here and not programs. You can always re-
install an application program and the copy on the hard disk
that is lost may have been infected.
MYTHS
There have been some reports, all of them unconfirmed, of
programs that are able to write to disks with the write
protect notch on. I beleive this to be absolute nonsense and
probably caused by delayed disk writes from cache programs or
floppy serial numbers being the same. When writing my disk
formatter (AFMT), I had to bypass the operating system and
access the hardware directly and never managed to write to a
write protected disk.
(From the Western Digital 1772 Disk Controller Data Sheet)
"Write protect: This input is sampled whenever a
Write Command is received. A logic low on this line
will prevent any Write Command from executing
(internal pull-up)."
The only way this could be circumvented would be to modify the
disk drive or its connection to the computer. However I am
open minded enough to beleive this phenomenon if and when I
ever see it and you can be pretty sure I'll tell you if I do!