What is a Computer Virus?

One the most common questions I get from friends and customers is, “What is a Computer Virus?” The short answer is, “A computer virus is a small program that is designed to interfere with the operation of your computer. The more difficult question is, “Why?” That unfortunately is a much more difficult question to answer. Why does anyone do malicious things? Some reasons include:

* To take control of a persons computer or network
* To generate money
* To steal sensitive information (Credit Card information, passwords, etc.)
* To prove it can be done or exact revenge
* To cripple a computer or network

Taking Control of a Computer

This is perhaps one of the most common types of viruses. Typically classified as ‘Trojans’ these viruses are mostly unknowingly downloaded via email or shared files from the Internet. The computer user believes the file is a legitimate one only to find out it is a virus.

Once the computer is infected, the Trojan can join a private chat network in the background unbeknownst to the user and await activation. Once activated by the Trojan creator, the virus can use your computer along with thousands of others to lodge an attack against another computer or network. The Trojan creator remains anonymous while your computer is used as a tool for attacking someone else.

Generate Money

In my experience, this type of infection masquerades itself as a Virus Removal Tool. It typically begins as a pop up ad indicating there are infections on your computer. Once activated, usually by the user who believes they are doing the right thing, the Virus will “Scan” your computer, indicate there are multiple infections, and offer to remove the infections upon purchase of the software. Upon purchasing, not only does the user either not get any software or get very low quality software, but the user has now provided their credit card and billing information to the creator. A very common instance of this type of virus is “AntiVirus 2009/2010”

Steal Sensitive Information

These types of viruses can sniff the traffic going in or out of a computer for interesting information such as passwords or credit card numbers and send it back to the virus creator. These types of viruses often use key logging as a method of stealing information where it maintains a record of everything that is typed into the computer such as emails, passwords, home banking data, instant messenger chats etc. This type of virus can be very effective in helping the creator steal the identity of the user.

To Prove a Point

Some virus creators simply want to show that it can be done. It is the ultimate display of ego for a virus author to find out that their virus has infected enough computers to become a real nuisance, show up on Google or even the news. Some virus creators also want to demonstrate that the Microsoft Windows Operating System is easily exploitable. A perfect example of this is the infamous MS.Blaster virus, also know as “Lovesan.”

To Cripple a Computer or Network

Few viruses now days are intended to disable a computer because it stops viruses ability to spread to other computers. Computer crippling viruses still exist, but nowhere near as common as the viruses mentioned above. The worst type of computer crippling viruses were back in the days of the 486 computers where the virus would overwrite the Master Boot Record (MBR) of the computer which would often prevent the computer from starting up at all.

Unlike computer crippling viruses, network crippling viruses are all too common now days. Most viruses that are designed to launch a Denial of Service attack will cause a significant load on a computer network, often bringing it down completely.