It's official

Mac OS X has its first real virus (or Trojan). This was bound to happen and hopefully Apple will take serious steps to address security in its OS.

I would say 75% of the reason why it's taken so long for an OS X virus to emerge has been due to a lack of interest on the behalf of virus writers- not because OS X is in some ways more secure than Windows (though it is).

A key aspect of the Mac experience is not having to deal with viruses and adware. Apple needs to make it a top priority to maintain this experience, and it's going to require a lot more proactive work now that OS X's profile is rising.