 Author:
Nada Sbaiti
Computing & Networking Services,
American University of Beirut
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What is a computer
virus?
A computer virus is a program - a piece of
executable code - that has the unique
ability to replicate. Like biological
viruses, computer viruses can spread
quickly and are often difficult to
eradicate. They can attach themselves to
just about any type of file and are spread
as files that are copied and sent from
individual to individual.
Besides replication, some computer viruses
have something else in common: a damage
routine that can deliver the virus payload.
While payloads may only display messages or
images, they can also destroy files,
reformat your hard drive, or cause other
kinds of damage. If the virus does not
contain a damage routine, it can still
cause trouble by taking up storage space
and memory, and downgrading the overall
performance of your computer.
Several years ago most viruses spread
primarily via floppy disk, but the Internet
has introduced new virus distribution
mechanisms. With email now used as an
important business communication tool,
viruses are spreading faster than ever.
Viruses attached to email messages can
infect an entire enterprise in a matter of
minutes, costing companies millions of
dollars annually in productivity loss and
clean-up expenses.
Generally, there are three main classes of
viruses:
- File infectors. These viruses
attach themselves to program files,
usually selected .COM or .EXE files. Some
can infect any program for which
execution is requested, including .SYS,
.OVL, .PRG, and .MNU files. When the
program is loaded, the virus is loaded as
well.
- System or boot-record
infectors. These viruses infect
executable code found in certain system
areas on a disk. They attach to the DOS
boot sector on diskettes or the Master
Boot Record on hard disks. A typical
scenario (familiar to the author) is to
receive a diskette from an innocent
source that contains a boot disk virus.
When your operating system is running,
files on the diskette can be read without
triggering the boot disk virus. However,
if you leave the diskette in the drive,
and then turn the computer off or reload
the operating system, the computer will
look first in your A drive, find the
diskette with its boot disk virus, load
it, and make it temporarily impossible to
use your hard disk. (Allow several days
for recovery.) This is why you should
make sure you have a bootable floppy.
- Macro viruses. These are among
the most common viruses, and they tend to
do the least damage. Macro viruses infect
your Microsoft Word application and
typically insert unwanted words or
phrases.
How to protect yourself against
viruses
The best protection against a virus is to know the
origin of each program or file you load into your
computer. Since this is difficult, you must install an
Antivirus software
configure
it to best adapt to AUBnet security
policies. The anti-virus software will
typically check all of your files
periodically and remove any viruses that
are found.
Hoaxes!
From time to time, you may get an e-mail
message warning of a new virus. Chances are
good that the warning is a virus hoax and
contain bogus information intended only to
frighten or confuse users. Please check
official virus watch sites before
forwarding such emails. Both McAFEE
and
Norton websites (external
links) have a section on
hoaxes.
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