Think MACs are Safe from Viruses - One in Five

One in five Mac computers is carrying malware that could spread to PCs, according to a new research from security vendor Sophos.

The security team ran its Mac antivirus software on 100,000 Mac computers. It found that most of the malware found is directed at Windows PCs, so Macs harboring the infections don't show any symptoms, unless perhaps the Mac is also running Windows. However, those computers can also spread malware to Windows PCs.

Sophos also found that one in 36 Macs, or 2.7 percent, were carrying Mac OS X malware. Of those, 75 percent harbored the Flashback malware. Numbers vary on Flashback's spread, but some estimates pegged the number at 650,000 Macs infected over the past few months. It's installed when it tricks users into downloading a fake version of Adobe (Nasdaq: ADBE) Flash Player. Apple (Nasdaq: AAPL) issued a Java update for Mac OS X to help remove the infection.

Another 18 percent of the Mac computers analyzed by Sophos were found with MacDefender scareware. The remaining threats included fake antivirus attacks, which can obtain credit card information from users.