"More than 600,000 Macs have been infected with a new version of the Flashback Trojan horse that's being installed on people's computers with the help of Java exploits, security researchers from Russian antivirus vendor Doctor Web said on Wednesday."Fast-growing Flashback Botnet Includes Over 600,000 Macs, Malware Experts Say
Technical details here: New Flashback Variant Changes Tack to Infect Macs
This is serious, folks. Run your "Software Update" now and reboot. Help your non-technical friends do it too.