The Flashback Trojan that has been infecting Mac OSX machines of late appears to have become the most successful piece of Mac-based malware in the short history of such things. Researchers say that there have been upwards of 500,000 Macs infected by the malware. Apple has now released a patch for the Java flaw that the Trojan exploits. The Trojan uses the same kind of drive-by download techniques that have plagued Windows users for a decade and injects code into running processes on the vulnerable Macs.
Source: https://threatpost.com/flashback-mac-trojan-hits-more-500k-machines-040512/76407/