As we've all known for some time, the vast majority of malicious hacks are aimed at Microsoft's Windows operating system and other products, largely because Microsoft has more than 90 percent of the market for computer operating systems. This worm, called OSX/Leap-A, is believed to be the first such virus aimed specifically at the Mac platform. It is spread through instant messaging and will not automatically infect Mac computers, but will ask users to accept the file.

"This first Macintosh OS X threat is an example of the continuing spread of malicious code on to other platforms," said Vincent Weafer, senior director at Symantec Security Response, in a statement.

Symantec ranked the new worm as a Level 1 threat (with 5 being the most severe).

Here is the OSX.Leap.A security response from Symantec.