“A recent version of malicious software called Flashback exploits a security flaw in Java in order to install itself on Macs. Apple has released software updates for systems running OS X Lion and Mac OS X v10.6 that will update Java to fix the security flaw, and remove the Flashback malware if it is present. A standalone update is also available for OS X Lion that will remove the Flashback malware from systems that do not currently have Java installed.” About Flashback Malware – Apple
Laurent Garnier: Flashback (1997)
Download a handy little AppleScript to detect and remove Flashback.