Apple's Mac OS X remains almost completely free of any sort of malware threat despite several years of availability, a significant market share, and even an entire month dedicated to pointing out its flaws. 

And security experts are not exactly sure why. In an article for the McAfee Avert Labs blog, security researcher Marius van Oers pointed out that Mac malware is "pretty much non-existent at the moment". 

The researcher said that out of 236,000 known pieces of malicious software, only seven affect Mac OS X.

"With an estimated OS X market share of about five per cent on desktop systems we would expect to see more malware for OS X," said van Oers.

The Mac OS X system is not inherently more secure than other operating systems, according to the researcher.

The Unix/BSD code on which OS X is based is fairly well known, and van Oers noted that there are more than 700 pieces of malware targeting various Unix and Linux platforms.

Vulnerabilities in OS X are also plentiful. Apple's most recent update patched more than 30 security flaws.  

But van Oers pointed out that many malware authors simply prefer to target the low-hanging fruit of a poorly maintained Windows system.

"Microsoft's Windows is dominant in the desktop market and it is clear why most malware is written for it," said van Oers. 

"Also, prior to Vista, the various Windows versions were pretty much wide open, full access, making it relatively easy for malware to abuse."

The researcher warned, however, that the days of widespread attacks seeking to infect as many PCs as possible are over.

Old virus-style malware has been replaced by newer programs that aim to covertly infect specific groups of machines and build money-making botnets.

"Nowadays malware writers do not go for massive attacks but tend to focus on targeted attacks," explained van Oers.

"This is more worrisome then the poor malicious demonstrators that the OS X threats of Leap and Macarena really represent. Nevertheless it is clear that OS X malware is not taking off yet."