Update: not as big a threat as originally thought. more details are here
So much for happy times in OS-X land. The first worm going after Mac users has been unleashed and targets users of the Macintosh OSX 10.4 operating system. OSX.Leap.A is a Level 1 threat (on a scale of 1 to 5, with 5 being most severe).It is a worm that spreads via the iChat instant messaging program and makes use of the Spotlight search program, included in OSX, and will run each time the machine boots.
Vincent Weafer, senior director at Symantec Security Response says that “this worm will not automatically infect, but will ask users to accept the file, giving potential victims a heads up and the opportunity to avoid infection. The important piece of advice for any iChat users running OSX 10.4 is not to accept file transfers, even if they come from someone on a buddy list.”
Additional details at: http://securityresponse.symantec.com/