Ten months after it debuted rudimentary malware scanning in Snow Leopard, Apple this week quietly added a signature for a third piece of malware, security researchers reported today.

According to U.K-based antivirus vendor Sophos and U.S. Mac security company Intego, Mac OS X 10.6.4 , which Apple released this past Tuesday, includes an update to XProtect.

Dubbed that because the malware signatures are contained within Snow Leopard's "XProtect.plist" file, the feature debuted in August 2009 with the launch of Mac OS X 10.6 . At the time, Apple included detection for only two pieces of malware, Trojan horses named "RSPlug.a" and "Iservice" by Symantec.

The 10.6.4 update added a scanning signature for another Trojan, which Symantec has labeled as "HellRTS."

More: http://pcworld.com/article/199288/