MacDefender Malware Protection and Removal Guide
The MacDefender malware has been causing trouble for Mac users all over the world; people are calling Apple Support in a panic, spending time visiting their local Apple Store Genius, and getting all stressed out about it. What's worse: the malware is mostly harmless. It's a scam trying to rip off your credit card number, not hurt your Mac.
The attack, which displays a message stating that your machine has been infected with viruses that only a "MacDefender" app can remove, has been spreading rapidly. MacDefender doesn't infect Macs with a virus, nor does it run a keylogger as a background process on your machine. It's simply trying to scare users into providing credit card information by registering an unneeded piece of software. MacSecurity and MacProtector are the same scam software, differing in name only.
It's been reported by ZDNet's Ed Bott that Apple is telling support reps not to assist with removing this malware. You're on your own, but TUAW is here to help you.