A program called MACDefender has been gaining victims as more and more Apple users download it.

The creators of MACDefender worked on getting the site high in search results for unrelated phrases. This gained victims by taking them from the search page of the unrelated phrase to the MACDefender page, which would pretend to scan the machine and tell them that they have a security threat, asking for cash before the problem was solved.

The site would launch the browsers of unattended machines and launch pornographic websites – the ‘threat’, urging people to pay to resolve the problem.

Apple's forums have been full of threads for information on how to remove the software from the users machine.  

Graham Cluley, senior technology consultant at Sophos said "Although there is much less malware in existence for Mac OS X than there is for Windows, that's no reason to put your head in the sand and think that there are no Mac threats out there,"