A virus is a program that has two functions: proliferate (make more
copies of itself) and activate (at some signal count, date, and so
on, do something-usually something bad like delete the boot sector).
A virus does not have to do damage to be a virus.
Boot sector viruses change the code in the master boot record (MBR)
of the hard drive.
Executable viruses reside in executable files. They are literally
extensions of executables and are unable to exist by themselves.
Macro viruses are specially written application macros. These viruses
will auto-start when the particular application is run and will then
attempt to make more copies of them-selves.
Trojans are true, freestanding programs that do something other than
what the person who runs the program thinks they will do. An example
of a Trojan would be a program that a person thinks is a game but
that is actually a CMO eraser. Some Trojans are quite sophisticated.
It might be a game that works perfectly well, but when the user quits
the game, it causes some type of damage.
A worm is a very special form of virus. Unlike all of the other viruses
described, a worm does not infect other files on the computer. Instead,
a worm replicates by making copies of itself on other systems on a
network by taking advantage of security weaknesses in networking protocols.
A bimodal or bipartite virus uses both boot-sector and executable
The only way to protect your PC permanently from getting a virus is
to disconnect from the Internet and never permit any potentially infected
software to touch your precious computer. Because neither scenario
is likely these days, you need to use a specialized antivirus program
to help stave off the inevitable virus assaults.
A polymorphs virus attempts to change its signature to prevent detection
by antivirus programs, usually by continually scrambling a bit of
The term “stealth” is more of a concept than an actual
virus function. Most stealth virus programs are boot sector viruses
that use various methods to hide from antivirus software.
The secret to preventing damage from a virus attack is to keep from
getting one in the first place. As discussed earlier, all good antivirus
programs include a virus shield that will automatically scan floppies,
downloads, and so on. Use it. It is also a good idea to scan a PC
daily for possible virus attacks. Again, all antivirus programs include
TSRs that will run every time the PC is booted. Last but not least,
know where software has come from before you load it. Although the
chance of commercial, shrink-wrapped software having a virus is virtually
nil (a couple of well-publicized exceptions have occurred), that illegal
copy of “Unreal Tournament” you borrowed from a local
hacker should definitely be inspected with care.
Get into the habit of having an antivirus floppy disk-a bootable,
copy-protected floppy with a copy of an antivirus program. If you
suspect a virus, use the diskette, even if your antivirus program
claims to have eliminated it. Turn off the PC and reboot it from the
antivirus diskette. Run your antivirus program’s most comprehensive
virus scan. Then check all removable media that were exposed to the
system and any other machine that may have received data from, or
is networked to, the cleaned machine. A virus can often go for months
before anyone knows of its presence.
Every PC gets slower and stodgier overtime. You load and unload programs,
you download stuff off the Internet, the system crashes and scatters
temp files all over the place-all of these factors contribute to the
decline of snappiness. Sometimes the decline comes in a more dramatic
fashion, though. A client of mine recently bought a new Pentium 4
system with all the bells and whistles.