But what is making the free-to-use and freemium programs so popular all of a sudden? After all, free antivirus suites have been around for years but have tended to be seen as the poor relations to paid software.

One answer is simply the influence of Microsoft Security Essentials, a totally free program launched by Microsoft in 2009 after fitful and generally failed attempts by the company to sell paid antivirus protection going back to the days of Windows XP.

The software has been given generally good reviews, despite a recent independent test that put it near the bottom in terms of its . Many users might see it as a zero-cost way of getting perfectly adequate protection from a brand that is guaranteed to stick around.

A second and intriguing possibility in an age where fake antivirus programs have become one of the biggest malware issues of the Internet, is that there has been a flight to the safety of better-known brands that don't demand a subscription fee. Certainly, the market remains hugely fragmented and confusing for consumers, which could be fuelling a gradual consolidation.

"In North America, fifty-one different antivirus vendors were detected in this report. The top five of those vendors combined to control 62.8 percent of the antivirus market," OPSWAT's analysis notes. "The worldwide market is slightly more distributed, with sixty-two vendors and 58.2 percent of the antivirus market controlled by the top five vendors."