Many viruses have been written before and probably after you
read this article. A few names include the Israeli, Lehigh, Pakistani
Brain, Alameda, dBase, and Screen. Keep in mind that most viruses
ONLY infect COM and EXE files, and use the Operating System to spread
their disease. Also, many viruses execute their own code before the
host file begins execution, so after the virus completes passive
execution (without "going off") the program will load and execute
normally.
Israeli - This one is a TSR virus that, once executed, stayed in
memory and infected both COM and EXE files, affecting both HARD and
FLOPPY disks. Once executed, the virus finds a place to stay in the
system's memory and upon each execution of a COM or EXE file, copies
itself onto the host phile. This one is very clever, before infecting
the file, it preserves the attributes and date/time stamp on the
file, modifies the files attributes (removes READ only status so it
can write on it), and then restores all previous values to the file.
This virus takes very little space, and increases the host file size
by approximately 1800 bytes. The trigger of this virus is the date
Friday the 13th. This trigger will cause the virus to either trash
the disk/s or delete the files as you execute them, depending on the
version. Whoever wrote this sure did a nice job....
Lehigh - This one infects the COMMAND.COM file, which is always
run before bootup, so the system is ready for attack at EVERY bootup.
It hides itself via TSR type and when any disk access is made, the
TSR checks the COMMAND.COM to see if it is infected. Then if it
isn't, it infects it, and adds a point to its counter. When the
counter reaches 4, the virus causes the disk to crash. This one,
however, can be stopped by making your COMMAND.COM Read-Only, and the
date/time stamp is not preserved, so if the date/time stamp is
recent, one could be infected with this virus. This virus is
transferred via infected floppy disks as well as a clean disk in an
infected system. It can not infect other hosts via modem, unless the
COMMAND.COM is the file being transferred.
Pakistani Brain - This one infects the boot sector of a floppy
disk. When booting off of the disk, the virus becomes a TSR program,
and then marks an unused portion of the disk as "bad sectors." The
bad sectors, cannot be accessed by DOS. However, a disk directory of
an infected disk will show the volume label to be @ BRAIN. A CHKDSK
will find a few bad sectors. When you do a directory of a clean disk
on an infected system, the disk will become infected. The virus has
no trigger and immediately begins to mark sectors bad even though
they are good. Eventually, you will have nothing left except a bunch
of bad sectors and no disk space. The virus itself has the ASCII
written into it with the words "Welcome the the Dungeon" as well the
names of the supposed authors of the virus, and address, telephone
number, and a few other lame messages. To inoculate your system
against this virus, just type 1234 at byte offset location 4 on the
boot track (floppy disks).
Alameda - This virus also infects the boot sector of the host
system. It is very small and inhabits ONE sector. This one only
damages floppy disks. If you boot from a diseased disk, the virus
loads itself into HIGH memory and during a warm boot, it remains in
memory and infects any other clean disks being booted from on the
infected system. It then replaces the boot track with the virus track
and replaces the boot track on the last track of the disk, so any
data located on the last track is corrupted. All floppy disks
inserted during reboot can catch this virus. This virus only infects
IBM PC's and XT's, however, it does not infect 286's or 386's.
dBase - This one is a TSR virus that works in a manner similar
to the Israeli virus. It looks for files with a DBF extension, then
it replicates itself in all DBF files, preserving file size, and all
attributes. After the first 90 days, the virus destroys your file
allocation table and corrupts all data in the DBF files. This virus
creates a hidden file, BUG.DAT that indicates the bytes transposed
(in order to preserve file specifications). Run a CHKDSK to make sure
you don't have any extra hidden files or a BUG.DAT in your dBase
directory. If you create a BUG.DAT file manually in your directory,
making it read-only, you will be safe from this virus.
Screen - This one is another TSR virus that comes on and off
periodically. When it is on, it examines the screen memory and looks
for any 4 digits starting at a random place on the screen. Then it
transposes two of them, this is not a good thing. It infects every
COM file in your directory, HARD and FLOPPY disks can be infected.
You can use a ASCII searcher to check if you are infected by
searching for "InFeCt" in your COM files. If you have this written,
read the 4 bytes immediately preceding it and overwrite the first 4
bytes of the program with their value. Then, truncate the program at
their stored address. You will rid yourself of this virus. Make sure
you use a clean copy of you editor for this.
Other viruses include MAC, AMIGA, and many other environments.
By the way, other computer systems other than IBM/DOS may become part
of CPI if you qualify.
Anyway, these are a few viruses I have read on and thus passed
the information to you, I hope you can learn from them and get some
ideas for some.
Downloaded From P-80 International Information Systems 304-744-2253
