Computer viruses

Types of virus

From worms to macros, there's a whole host of viruses out there to catch...

Worms

These viruses spread via computer networks. The ILOVEYOU virus was a classic example of a worm. These viruses are becoming an increasing threat as a growing number of computers are permanently connected to networks. Worms can spread over corporate networks or via emails sent over the Internet.

Trojans

A Trojan virus takes its name from a story in Homer's Iliad where Greek soldiers pretended to make peace with their enemies, the Trojans. The Greeks made a grand peace-keeping gesture - the gift of a large wooden horse.

When the Trojans hauled it inside their city gates, a small band of Greek warriors leapt out. They opened the gates and let the rest of the Greek army storm in to capture the city.

A Trojan virus is one that opens your computer up to malicious intruders, allowing them to read your files.

File viruses

A file virus is one that replaces a key system file on your computer. These viruses can reload themselves every time you start your computer up. Once they're in the memory, they can spread by writing themselves to any disk you insert into your disk drive.

Boot sector viruses

This is an early type of computer virus that spreads by hiding itself in an invisible location on your hard drive or floppy disk. When your computer reads an infectedfloppy disk, the virus is copied from the disk to your computer's memory.

From there, it writes itself to the 'boot sector' on your hard drive. The boot sector is read each time you turn your computer on. So the virus is constantly reloaded and can copy itself on to other floppy disks. These viruses are fairly rare nowadays, as they are easy to catch.

Macroviruses

A macrovirus infects word processor files, such as Microsoft Word documents. Although not as dangerous as other viruses, they can spread quickly if a Word file is sent via email. After an initial scare, Microsoft added protection into later versions of Word, so you receive a warning about infected documents.

Hoaxes

The virus hoax came about after friends sent each other emails about a new virus threat. Someone decided that they could cause just as much trouble by sending out fake warnings rather than real viruses.

Hoaxes may seem harmless, but they do a great deal of damage to the Internet as a whole. Not only do they slow down traffic and clog up email servers, but they also cause people to panic. Companies can spend money and time investigating what is just someone's idea of a joke.

Who Writes Computer Viruses?

Virus authors are normally 14-26 year old males who spend a lot of time on their computers. Some of them want to prove they are good programmers. Others want to show that they have the power to cause large-scale problems.

But most viruses don't constitute good programming, as many fail to deliver their payload. Many are re-hashed versions of old programs that require little skill to produce.

In the UK, if you're caught using a computer for criminal reasons you can receive a five-year sentence and an unlimited fine. If convicted of 'cyber-terrorism', then you can be given the same sentence as a terrorist bomber.

How do you catch a virus writer? Although the Internet allows computer viruses to spread quickly, it also helps to catch the authors.

Each computer connected to the Internet has an address, similar to a phone number. This is called an IP address and looks like this: 128.5.10.64. Every email you send is marked with your IP address and this information is hard to remove.

Your IP address reveals what company (or Internet Service Provider) holds your account. The company can then find out which customer sent the mail. So if you send a virus to a Member of Parliament, it won't be long before the police are knocking on your door asking questions.

Sophisticated virus authors would be able to cover their tracks to some degree, but there is usually some way to track them down.

Hackers, crackers and script kiddies

There's a whole zoo of cantankerous coders out there:

 Hackers: people who try to find security flaws in corporate computer programs. Most hackers don't aim to cause problems, but they might send an anonymous email to the person in charge warning them of their security problem. Amongst other hackers, there is much honour to be gained by those who can 'crack the uncrackable' programs

 Crackers: unlike hackers, crackers are less sophisticated. They like to break into people's websites and replace their corporate homepage either with pornographic images or hoax messages

 Script kiddies: young virus pirates, who copy old computer viruses and modify them. Often they don't work. If they do, they are seldom as dangerous as the originals and can be easily destroyed

From BBC site