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About viruses: Most antivirus tools today work by scanning for specific known viruses, looking for "signatures" such as particular file names or certain types of email attachments. But with as many as a dozen major vendors issuing regular signature updates, keeping hundreds of desktops and servers up-to-date can be more work than busy support staffs can handle.

What's a "Virus"? Computer viruses are called viruses because they share some of the traits of biological viruses. A computer virus passes from computer to computer like a biological virus passes from person to person. There are similarities at a deeper level, as well. A biological virus is not a living thing. A virus is a fragment of DNA inside a protective jacket. Unlike a cell, a virus has no way to do anything or to reproduce by itself, it is not alive. Instead, a biological virus must inject its DNA into a cell. The viral DNA then uses the cell's existing machinery to reproduce itself. In some cases, the cell fills with new viral particles until it bursts, releasing the virus. In other cases, the new virus particles bud off the cell one at a time, and the cell remains alive.