One of the most common questions I get from friends and clients is: “What is a computer virus?” The short answer is: “A computer virus is a small program that is designed to interfere with the way your computer works. The more difficult question is: “Why?” Unfortunately, that is a much more difficult question to answer. Why does someone do malicious things?
* To take control of a person’s computer or network
*To generate money
* To steal confidential information (credit card information, passwords, etc.)
* To show that it can be done or revenge
* To paralyze a computer or network
Take control of a computer
This is perhaps one of the most common types of viruses. Normally classified as ‘Trojans’, these viruses are mostly downloaded unknowingly via email or Internet file sharing. The computer user believes that the file is legitimate only to discover that it is a virus.
Once the computer is infected, the Trojan can join a private chat network in the background without the user’s knowledge and wait for activation. Once activated by the Trojan’s creator, the virus can use your computer along with thousands of others to carry out an attack against another computer or network. The creator of the Trojan remains anonymous while his computer is used as a tool to attack another person.
generate money
In my experience, this type of infection masquerades as a virus removal tool. It usually starts as a pop-up ad stating that there are infections on your computer. Once activated, usually by the user who thinks they are doing the right thing, the virus will “scan” their computer, report multiple infections, and offer to remove the infections upon purchase of the software. When making the purchase, the user not only gets no software at all or gets very low-quality software, but they have 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 confidential information
These types of viruses can track traffic entering or leaving 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 keylogging as a method of stealing information in which they keep a record of everything that is typed on the computer, such as emails, passwords, home banking details, IM chats, etc. This type of virus can be very effective in helping the creator to steal the identity of the user.
to prove a point
Some virus writers simply want to show that it can be done. It’s the ultimate display of ego for a virus author to discover that his virus has infected enough computers to become a real nuisance, appear on Google or even in the news. Some virus writers also want to prove that the Microsoft Windows operating system is easily exploitable. A perfect example of this is the infamous MS.Blaster virus, also known as “Lovesan”.
To paralyze a computer or network
Few viruses today are designed to disable a computer because it stops the ability of viruses to spread to other computers. Computer crippling viruses still exist, but not as common as the viruses mentioned above. The worst type of computer crippling virus dated back to the days of 486 computers, where the virus would overwrite the computer’s Master Boot Record (MBR), often preventing the computer from booting.
Unlike computer crippling viruses, network crippling viruses are very common today. 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 entirely.