Also called "rogueware," scareware is bogus security software that claims a computer is heavily infected with worms, viruses and other malware. Once installed, the worthless program nags users with pervasive pop-ups and fake alerts until they fork over a fee. MacDefender, the generic name for the new series that targets Macs, demands $60 to $80 to cease and desist.

in early May, but since then several variants have appeared, including MacGuard, which installs without requiring a password.

The new MacDefender appeared only hours after Apple issued its update yesterday, said James.

"They'll keep doing this," James predicted, referring to the cat-and-mouse game between the hackers who create MacDefender and Apple's efforts to block them.

"It's worked well enough that they're making money off it, or they wouldn't be doing this. Coming out with a new version right after the update, and a new version as soon as Apple announced it was going to release an update, shows that they're planning on staying on top of things," James said.