A (not so) brief introduction to computer viruses

How does a virus work?
That really depends on the type of virus, there are several basic types. In no particular order of importance, they are:

• Boot Sector Viruses – The first part of a disk; be it floppy, hard drive, or CD / DVD; is called the boot sector. Boot sector viruses take up residence in this part of the disk and infect anything that it comes in contact with. This was one of the first types of viruses. If a user booted from an infected floppy, it would infect the computer.
• File – File viruses act like parasites. They attach to other files and, as that file is accessed, they spread.
• Macro / Script – Macro viruses are some of the easiest to create, therefore they are all over the place. When programs started adding macro languages it was just a matter of time before someone wrote a virus as a macro. Microsoft Office in particular makes it easy to write a virus and have it spread through email.
• Polymorphic – A polymorphic virus is one that can change its signature to elude virus scanners. Most viruses are recognized by their signature, but if it is constantly mutating they are harder to detect.
• Trojan Horse – A trojan horse is a similar idea to its namesake. It is a program that acts as though it is doing one task, but is actually doing another. It may be capturing keystrokes, looking for your bank information in Quicken, deleting files, sending out spam to other users, or taking part in DDoS attacks.
• Worm – A worm creates a copy of itself and then communicates with other copies of itself. These are common in DDoS attacks. Think of thousands of worms crawling through dirt. That’s what these worms look like on the internet.

As you can see, there is some overlap in these types. Just because a virus is a “worm”, or “trojan”, or “boot sector” does not exclude it from being categorized in other groups. A virus that falls into multiple groups is called multi-partie.

Who writes viruses?
All sorts of people write viruses. The authors of the Brain virus wrote it to limit piracy of their software. Others write as a political message. Some write simply to play a joke.

However, the most dangerous situation comes when someone is trying to prove themselves. Virus writers belong to their own counter-culture. Often they try to upstage each other. That happened this year when the authors of the Netsky and Bagle series of viruses competed with each other to see whose virus could have the biggest impact.

To get into a blatent generalization: a typical virus writer is a under 25-year-old male, single, and ties their self-esteem to their peer group. In most of these cases the peer group is an electronic group rather than a true circle. Virus writing has been compared to graffiti. It is something done to “impress” others.

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