All About Computer Viruses
Your computer is as slow as molasses. Your mouse
freezes every 15 minutes, and that Microsoft Word
program just wont seem to open.
You might have a virus.
Just what exactly is a virus? What kind is in your
computer? How did it get there? How is it spreading
and wreaking such havoc? And why is it bothering with
your computer anyway?
Viruses are pieces of programming code that make
copies of themselves, or replicate, inside your computer
without asking your explicit written permission to
do so. Forget getting your permission down on paper.
Viruses dont bother to seek your permission
at all! Very invasive.
In comparison, there are pieces of code that might
replicate inside your computer, say something your
IT guy thinks you need. But the code spreads, perhaps
throughout your office network, with your consent
(or at least your IT guys consent). These types
of replicating code are called agents, said Jimmy
Kuo, a research fellow with McAfee AVERT, a research
arm of anti-virus software-maker McAfee Inc.
In this article, though, were not talking about
the good guys, or the agents. Well be talking
about the bad guys, the viruses.
A long, long time ago in computer years, like five,
most viruses were comprised of a similar breed. They
entered your computer perhaps through an email attachment
or a floppy disk (remember those?). Then they attached
themselves to one of your files, say your Microsoft
When you opened your Microsoft Word program, the
virus replicated and attached itself to other files.
These could be other random files on your hard drive,
the files furthest away from your Microsoft Word program,
or other files, depending on how the virus writer
wanted the virus to behave.
This virus code could contain hundreds or thousands
of instructions. When it replicates it inserts those
instructions, into the files it infects, said Carey
Nachenberg, Chief Architect at Symantec Research Labs,
an arm of anti-virus software-maker Symantec. Corp.
Because so many other types of viruses exist now,
the kind just described is called a classic virus.
Classic viruses still exist but theyre not quite
as prevalent as they used to be. (Perhaps we could
put classic viruses on the shelf with Hemingway and
These days, in the modern era, viruses are known
to spread through vulnerabilities in web browsers,
files shared over the internet, emails themselves,
and computer networks.
As far as web browsers are concerned, Microsofts
Internet Explorer takes most of the heat for spreading
viruses because its used by more people for
web surfing than any other browser.
Nevertheless, Any web browser potentially has
vulnerabilities, Nachenberg said.
For instance, lets say you go to a website
in IE you have every reason to think is safe, Nachenberg
But unfortunately it isnt. It has virus code
hidden in its background that IE isnt protecting
you from. While youre looking at the site, the
virus is downloaded onto your computer, he said. Thats
one way of catching a nasty virus.
During the past two years, another prevalent way
to catch a virus has been through downloads computer
users share with one another, mostly on music sharing
sites, Kuo said. On Limewire or Kazaa, for instance,
teenagers or other music enthusiasts might think theyre
downloading that latest Justin Timberlake song, when
in reality theyre downloading a virus straight
into their computer. Its easy for a virus writer
to put a download with a virus on one of these sites
because everyones sharing with everyone else
Heres one you might not have thought of. If
you use Outlook or Outlook Express to send and receive
email, do you have a preview pane below your list
of emails that shows the contents of the email you
have highlighted? If so, you may be putting yourself
Some viruses, though a small percentage according
to Nachenberg, are inserted straight into emails themselves.
Forget opening the attachment. All you have to do
is view the email to potentially get a virus, Kuo
added. For instance, have you ever opened or viewed
an email that states its loading?
Well, once everything is loaded, a virus
in the email might just load onto your computer.
So if I were you, Id click on View on the toolbar
in your Outlook or Outlook Express and close the preview
pane. (You have to click on View and then Layout in
On a network at work? You could get a virus that
way. Worms are viruses that come into your computer
via networks, Kuo said. They travel from machine to
machine and, unlike, the classic viruses, they attack
the machine itself rather than individual files.
Worms sit in your working memory, or RAM, Nachenberg
OK, so weve talked about how the viruses get
into a computer. How do they cause so much damage
once theyre there?
Lets say youve caught a classic virus,
one that replicates and attacks various files on your
computer. Lets go back to the example of the
virus that initially infects your Microsoft Word program.
Well, it might eventually cause that program to crash,
Nachenberg said. It also might cause damage to your
computer as it looks for new targets to infect.
This process of infecting targets and looking for
new ones could eventually use up your computers
ability to function, he said.
Often the destruction a virus causes is pegged to
a certain event or date and time, called a trigger.
For instance, a virus could be programmed to lay dormant
until January 28. When that date rolls around, though,
it may be programmed to do something as innocuous
but annoying as splash popups on your screen, or something
as severe as reformat your computers hard drive,
There are other potential reasons, though, for a
virus to cause your computer to be acting slow or
in weird ways. And that leads us to a new segment
the reason virus writers would want to waste
their time creating viruses in the first place.
The majority of viruses are still written by teenagers
looking for some notoriety, Nachenberg said. But a
growing segment of the virus-writing population has
other intentions in mind.
For these other intentions, we first need to explain
the backdoor concept.
The sole purpose of some viruses is to create a vulnerability
in your computer. Once it creates this hole of sorts,
or backdoor, it signals home to mama or dada virus
writer (kind of like in E.T.). Once the virus writer
receives the signal, they can use and abuse your computer
to their own likings.
Trojans are sometimes used to open backdoors. In
fact that is usually their sole purpose, Kuo said.
Trojans are pieces of code you might download onto
your computer, say, from a newsgroup. As in the Trojan
War they are named after, they are usually disguised
as innocuous pieces of code. But Trojans arent
considered viruses because they dont replicate.
Now back to the real viruses. Lets say we have
Joe Shmo virus writer. He sends out a virus that ends
up infecting a thousand machines. But he doesnt
want the feds on his case. So he instructs the viruses
on the various machines to send their signals, not
of course to his computer, but to a place that cant
be traced. Hotmail email happens to be an example
of one such place, Kuo said.
OK, so the virus writers now control these computers.
What will they use them for?
One use is to send spam. Once that backdoor is open,
they bounce spam off of those computers and send it
to other machines, Nachenberg said.
Thats right. Some spam you have in your email
right now may have been originally sent to other innocent
computers before it came to yours so that it could
remain in disguise. If the authorities could track
down the original senders of spam, they could crack
down on spam itself. Spam senders dont want
Ever heard of phishing emails? Those are the ones
that purport to be from your internet service provider
or bank. They typically request some information from
you, like your credit card number. The problem is,
theyre NOT from your internet service provider
or your bank. Theyre from evil people after
your credit card number! Well, these emails are often
sent the same way spam is sent, by sending them via
Of course makers of anti-virus software use a variety
of methods to combat the onslaught of viruses. Norton,
for instance, uses signature scanning, Nachenberg
Signature scanning is similar to the process of looking
for DNA fingerprints, he said. Norton examines programming
code to find what viruses are made of. It adds those
bad instructions it finds to its large database of
other bad code. Then it uses this vast database to
seek out and match the code in it with similar code
in your computer. When it finds such virus code, it
lets you know!
©2004 by Kara Glover
About the author: Kara Glover is a Computer Tutor
and Troubleshooter. You can find her articles and
tutorials on topics such as Microsoft Word®, Excel®,
and PowerPoint® on her website: http://www.karathecomputertutor.com
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