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Computer Viruses -- What are They? How to Prevent Them
by
David P. Cunningham, P.E.
Copyright 2002
A computer virus is an infectious agent which affects computers
just as a human virus affects people. And, just as some human
viruses are more dangerous than others, so it is with computer
viruses. Unlike human infectious viruses, however, computer
viruses are not of natural origin. They are created for the
malicious purpose they serve; to aggravate and torment those of
us who use and depend upon computers.
What is a Computer Virus ?
By definition a computer virus is a program which is intentionally
designed to recreate itself and spread within a computing
environment. There are other trouble causing creations such as
"worms", "Trojan horses", and "bombs" which, although not
strictly viruses, are lumped into the same stew. Typically,
viruses are created to hide their presence until they have done
their dirty work. All are created by programmers bent on mischief.
Thousands of viruses exist and have to be considered and
addressed. What really makes viruses dangerous is their ability
to do something which is beyond your control and without your
prior approval.
True viruses come in different forms and function in different
ways. Some are fairly benign and others are capable of wreaking
complete havoc upon computers and networks. At the very
least, they are annoying. At worst, they can totally trash your
computers and the network they run on. However, even so-
called benign viruses can be highly troublesome because they
occupy significant hard drive space, consume CPU resources,
and slow down computers.
Computer viruses attach themselves to other, legitimate, programs
to allow themselves to spread. Such programs as applications,
spreadsheets, or word processors can be hosts. A particularly
good example is the recent Melissa virus episode. An arrest
has been made and charges filed in connection with the episode
but tremendous inconvenience and economic harm resulted.
Viruses can also be hosted and transferred in the boot sector
(the information first loaded from removable disks), in files
downloaded from the internet, and in computer memory.
The computer virus "industry" began in about 1987 when several
viruses were created in university laboratories for legitimate
testing purposes. Today there are literally thousands of different
viruses. All true viruses, however, are of three basic types;
macro viruses, file infectors, and boot sector viruses. In addition
to true viruses we have to contend with "worms", "Trojan horses",
and "bombs". "Worms" simply replicate themselves on the
computers and across the network. They take up large amounts
of space and cause capacity problems. A "Trojan horse" is named
for the Greek myth about the wooden horse on rollers, containing
Greek soldiers, left for the Trojans to pull into the City of Troy.
After night had fallen, the Greek soldiers jumped out and opened
the gates to the city, allowing the Greek army to enter. Similarly,
a virus is buried inside a legitimate appearing program which
releases the virus once it enters the computer. Thus, it is called
a "Trojan Horse" A "bomb" is a program which is event driven
and, upon execution of an event, runs a script which does
something annoying or destructive. Unfortunately, virus writers
are making significant progress in making their "products" harder
to detect and potentially much more damaging.
How Do Viruses Spread ?
Like human viruses, computer viruses spread by contact. If
computers are physically isolated it takes an intermediary to
spread a virus: a contaminated floppy disk, an unscanned internet
download, a technician's diagnostic disks, and, yes, shrink
wrapped software. Many of the viruses introduced into business
computers come from contaminated floppy disks from home or
other businesses. Yes, you can be the victim of other's poor
sanitation practices. Other significant sources of contamination
are software programs or files downloaded from the internet.
No matter what the source, your computers are at significant
risk of contamination and require effective protection,
What are the Symptoms ?
Unusual events, including unexpected drive activity, strange
screen events, odd error messages, failure of a program to
execute properly and system bootup failures are one series of
symptoms. Another is unanticipated changes in file dates or time
stamps, in the length of programs, in memory or disk space or
in system load times. Sometimes the symptoms reveal an
unmitigated disaster and its too late to recover gracefully.
What's the Risk ?
The minimum risk is that a virus will occupy more and more
disk space and tie up increasing amounts of CPU resources until
your computer system slows to a crawl. The maximum risk is
that all your programs and data will be destroyed rendering your
computer system absolutely and totally useless. The difference
is, of course, the level of ultimate aggrevation but both are
unacceptable. It can take, on the average, 4-6 days to recover
from a virus attack. If you have no backup it is possible that
your business might never recover.
What Can You Do ?
First and foremost is active prevention. Install the best available
antivirus software available on your computers, keep it updated
and use it regularly. We recommend and use Norton Antivirus
5.0 by Symantec. It will search out and eliminate email, Web,
and compressed file viruses. And, frequent downloadable updates
are available from Symantec.
Educate your staff to the risk. Create and enforce a policy with
respect to non-company owned removable disks. Do not permit
the introduction of disks from any source outside of the mall,
especially any disks containing executable files or macros. Do
not allow any unscanned disks, no matter what the source, to be
used in your computers. Treat all downloaded internet files the
same way. Many malls have simply been lucky but luck has a
way of running out.
If, despite all of your precautions, you find yourself in the
unfortunate position of harboring a virus, get professional help.
Remember our advice ? Find a competent computer professional
and establish a good working relationship with him (or her) in
advance. It pays great dividends when you have seemingly
impossible to solve problems with your computer equipment.
It isn't a question of if you'll have problems; its when !
One parting thought. Your concern about and planning for the
prevention of a virus infection is well justified. However,
paranoia about viruses is neither justified nor necessary. Just
don't fail to take the precautions necessary. To do so is
akin to ignoring your own personal need for vaccinations.
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