According to Sophos, a recent update to Mac OS X secretly added protection against a Trojan.

"Buried in the code is an update to the XProtect.plist file, which contains signatures of malware written to target the Mac," writes CNET News' Elinor Mills. "The signatures now detect malware dubbed 'HellRTS,' Graham Clulely of Sophos wrote in a blog post."

"HellRTS, which Sophos detects as 'OSX/Pinheard-B,' is a Trojan that has been around several months," Mills writes.

Click here to read the CNET News article.