Two months ago, a new variant of the Flashback Trojan started exploiting a security hole in Java to silently infect Mac OS X machines. Apple has since patched Java, but this was only yesterday. As of today, more than 600,000 Macs are currently infected with the Flashback Trojan, which steals your user names and passwords to popular websites by monitoring your network traffic.I've been saying for a long while that this sort of thing was inevitable, and have been saying that Apple is pathetic in how slowly they patch security holes in Java - Microsoft patched this weeks and weeks ago.
If you run Mac OS X, you can find details on uninfesting your machine here. And remember that this is no longer operative: