Apple on Tuesday released an update for the Mac OS X operating system known as Snow Leopard 10.6.7 in response to a rogue anti-virus malware commonly known as MacDefender.

MacDefender is a form of Trojan Horse scareware that often infects Apple's Mac computers through poisoned image searches on sites like Google. Once it infects a computer, it takes over the desktop and is difficult to remove as it attaches itself to the launch menu and has no dock icon.

It initiates a third-party malware attack flashing pornographic images and the like, then prompts users to purchase an expensive anti-virus solution to be rid of the "threat."

This “solution” is called MacDefender, MacProtector, or MacSecurity and is linked to a Russian security researcher.

Apple's "Security Update 2011-003," adds a definition for the scareware called "OSX.MacDefender.A" in the operating system's File Quarantine Information malware check. If detected, MacDefender-class scareware is quarantined and removed from the system, with users getting an alert if this happens.

MacDefender started appearing in April of 2011.
Apple has in the past trumpeted the Mac's relative lack of malware problems as compared to Microsoft's Windows platform. But growing market share and Apple's increasing notoriety have apparently made OS X a juicy target for such security threats.