Apple has not added any anti-malware signature updates to the XProtect.plist file that launched with antidotes for OSX.RSPlug.A and OSXX.Iservice, two known Trojan horse programs targeting Mac OS X users. It only scans files downloaded with a handful of applications (Safari, Mail, iChat, Firefox, Entourage, and a few other Web browsers). It’s disappointing that Apple hasn’t seen it fit to expand the signature base to catch the growing list of DNS-Changer threats that specifically target the Mac.
Source: https://threatpost.com/apple-malware-blocker-left-dead-010410/73320/