Mac OS X is *nix
"Mac OS X is *nix"
Bingo. Mac is BSD. Mac has been safe for 2 reasons, small market share, and proprietary hardware. Now that OS X will run on Intel, and Mac seems to be gaining in market share, they will become a more attractive target.
However, the Mac zealots will point out, correctly, that for some time to come you'll still be safer on a Mac.
It is based on BSD Unix which was designed for DARPA
in the late 70s & 80s to be hack proof.