botnets

There hasn't been much press about it, but many websites (including this one) increasingly are under attack from zombie armies, clusters of Windows PCs that have been infected by viruses that allow them to be commanded and controlled remotely by spammers.

Typically a virus installs a "back door" on an infected PC that allows it to respond to remote commands. These commands are relayed through Internet chat systems in a chain designed to disguise the identity of the spammer.