Update April 12, 2012:
Apple has released new security updates that check for and remove the common Flashback malware variants. I highly encourage Snow Leopard and Lion users to run Software Update and get the official Apple tool.
What does it do?
Note This utility checks and reports the presence of Flashback malware, it does not remove it!
I have no affiliation with F-Secure or Apple.
Mac OS X 10.5 and up, PPC and Intel.