Viruses have been a thorn in the side of PC users since the late 1980's. The first computer virus was discovered in 1981 and was believed to have been spawned at Texas A&M. It is hard to estimate the number of viruses in the wild because new viruses are being created constantly. It is safe to say there are thousands of viruses currently active. Prior to the popularity of the Internet most viruses were spread on floppy disks.
There are many different types of viruses. As new tools are developed to combat viruses, virus writers come up with new ways to spread their creations. Some of the most common virus types are:
Basic - A basic virus is software created to attack computers via email or the Internet. Once a machine is infected it begins to infect other machines across the Internet. It may also attach itself to files stored on the computer's hard drive.
Trojan Horse - A trojan horse allows the creator to access your PC and steal data or use your PC for other activities. This is done by opening a 'back door' on your computer which the virus creator knows how to access. Trojan horses may or may not attach themselves to files on your hard drive.
Worm - A worm is similar to a basic virus in that it infects computers across a network or the Internet. Where worms differ is their ability to constantly spread. Worms can infect a computer without the user receiving an email or browsing the Internet. The best protection against worms is a firewall.
Combination - Beginning in the summer of 2003 viruses started to appear with all the characteristics of the above virus types. The 'SoBig' virus infected 1 out of every 2 emails sent at its height.
Worms and combination are currently the most rampant viruses on the