VIRUS - A computer virus will pass from one computer to another like a real life biological virus passes from person to person. For example, it is estimated by experts that the Mydoom worm infected a quarter-million computers in a single day in January 2004.Another example is the ILOVEYOU virus, which occurred in 2000 and had a similar effect. There are tens of thousands of viruses out there, and new ones are discovered every day. It is difficult to come up with a generic explanation of how viruses work, since they all have variations in the way they infect or the way they spread. So instead, we’ve taken some broad categories that are commonly used to describe various types of virus.