Microsoft has identified 13 different spamming operations that it claims use spam zombies. A zombie is a computer attached to a network that has had its security compromised and is remotely controlled for another purpose. This purpose may be to use it as a launching point for another attack, or the distribution of spam. Microsoft has filed suit against these spamming operations.

A lawsuit was filed against unnamed defendants in August. Since then Microsoft has tracked down some of the people behind the operations, said Tim Cranton, director of Internet Safety Enforcement Programs at Microsoft in Redmond, Wash.
Zombie PCs have become a serious problem; Microsoft believes more than half of all spam is sent by such systems.