According to a handful of dedicated hackers of Apple, Inc.'s (AAPL) computer operating system, OS X, the OS is actually less secure than Microsoft Corp.'s (MSFT) Windows.  But thanks to the OS's small market share (traditionally 5 percent or less) most cybercriminals haven't felt it worthwhile to target the platform.  Also, some hackers have misgivings about attacking Unix-like operating systems (e.g. Linux, OS X).

Still, Apple's growing market share and boastful claims of security have lead to an increased interest in attacks and some OS X malware has been popping up of late.  

The latest malware to target OS X is dubbed "MACDefender".  Attack pages for the new malware exploit the way Apple's default Safari browser handles Javascript, running a script that auto-initiates the download of a script file.  If the user has opted to open "safe" files, the archive will then auto-open and initiate an install dialogue.

The risk is minimal as users must approve of this dialogue and enter an administrative password to complete the installation.  Still it may be a bit more widespread as the attack pages have boosted themselves to near the top of many search results, thanks to search engine optimization (SEO) poisoning.

It is unclear what the software does when active, though it appears to be logging user activities.  Users who accidentally installed the software can still delete it by killing its process and dragging it from the Applications folder to the Trash bin.

Members of the Apple Support community first noted the malware last Saturday.  

On Monday, security firm Intego released an advisory, calling the risk of the malware "low".  Intego writes:

When a user clicks a link after performing a search on a search engine such as Google, this takes them to a web site whose page contains JavaScript that automatically downloads a file," Intego said. "In this case, the file downloaded is a compressed ZIP archive, which, if a specific option in a web browser is checked (Open 'safe' files after downloading in Safari, for example), will open.

The malware unfortunately shares its name with a legitimate OS X software firm.  MacDefender is a small software firm that makes geocaching software, including GCStatistic and DTmatrix.  The company has released a statement emphatically saying that it is not affiliated with the rogue software.

The company writes:

IMPORTANT NOTE: As it seams (sic) someone wrote a virus/malware application named mac defender (MacDefender.app) for OS X. If you see an application named like this DO NOT DOWNLOAD/INSTALL it. I would never release an application named like this.

In recent months botnet-forming worms and trojans have targeted OS X.  Most of these pieces of malware have been amateurish efforts, though, or works in progress.  Nonetheless it remains a very real possibility that Apple could one day see a serious attack.

For its part Apple has suggested users get an antivirus program, though it still claims in advertisements that its platform does not suffer from malware like Windows.  Apple has refused to provide customers with free antimalware software like Microsoft does, so security firm Sophos Plc. has picked up the ball offering free basic protection to Mac users.  Some other smaller firms also offer free Mac antimalware suites.