Creating a computer virus is no easy trick. Just like computer games and word-processing software, a virus is a program, or step-by-step instructions that tell a computer what to do. Unlike games and other software, however, a virus attaches itself to other programs in your computer and is essentially a digital parasite.

A virus contains instructions that tell it to self-replicate, or copy itself over and over again. When it first enters your computer through an infected floppy disk, e-mail, or a program downloaded from the Internet the virus copies itself to your computer's memory. Fro

This is a vicious cycle that continues so viruses have been put into categories. One category is a boot sector virus, which is probably the most common type of virus in that it resides on the boot sector of a floppy disk and then becomes transferred to the partition sector or DOS boot sector on a hard drive. The only way the computer will become infected with the virus is if the computer is started from the infected disk.

Some other types of viruses include network viruses that propagate by attaching themselves to network protocols, Trojan horse viruses well not actually a virus, but rather a program that claims to do something useful and instead damages the computer or system. Another similar program called a worm virus run independently and travels across networks carrying viruses. Worms typically hide and are transported when exchanging information over the Internet or through floppy disks. Viruses that belong to these categories may have additional characteristics that make them harder to detect and eliminate. Some of these characteristics include encryption, stealth, polymorphism, and time-dependence.

Many thousands of viruses

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