This Halloween ask yourself what's more frightening, being chased by an undead corpse that wants to eat your brain or having your PC slow to near-dead because it's been turned into an unwitting spam server?

Hey, a zombie's a zombie.

Unfortunately, the zombies that have taken over swaths of cyberspace are causing more harm than their brethren of horror-film fame. The latter is a person who is believed to have died and been brought back to life without speech or free will, which pretty much describes the cyber zombie, too, as it silently spits out spam unbeknownst to its owner.

"There are thousands of new machines infected [by zombies] each day, but no one really knows just how many," says Dave Rand, CEO of Kelkea, a company that sells software called Zombie Killer. (Rand laughs off the fact that his product's name is a misnomer, given that zombies are already dead.)

The term zombie, as it applies to computers, was coined in the late 1990s when these compromised PCs were used to perform denial-of-service attacks by pinging Web sites. They were called zombies because "the PCs would literally rise from the dead and someone could take over the operation of the machine," Rand says.