After years of Apple users claiming that their machines were more secure than Windows, it turns out that they just did not know what malware looked like.

Insecurity experts at Sophos say that there is a disturbingly high level of malware on Mac computers. After looking at 100,000 Mac computers running its free anti-virus software, Sophos discovered that 1 in 5 Mac computers had installed malware. While the machines would not cause symptoms of the Malware unless users also run Windows on their computer, it could still be spread to other computers.

More disturbingly, Sophos's analysis also shows that 2.7 per cent of Macs were found to be carrying Mac OS X malware. Graham Cluley, senior technology consultant at Sophos said that Mac users need a loud wake-up call about the growing malware problem on their computers.  Actually we think they need a good shaking and a clip around the ear with the hammer.

Part of the problem is that mac users are so technologically illiterate that they think a nice case means that a computer is good. For years there had been a myth that Steve Jobs's superior security was protecting the machines from infection when it was more luck and the fact that the writers of malware did not target mac users because they had nothing on their machines worth stealing.

Fake anti-virus attacks, which scare users into handing over their credit card details, and the recent 600,000 strong Flashback botnet dominate the chart of Mac-based threats.