If there is still any doubt at all about the security of Mac OS X, I think we are about to find out. Someone at the Army has resurrected an old idea. They're going to start using more Macs because...
"...fewer attacks have been designed to infiltrate Mac computers, and adding more Macs to the military's computer mix makes it tougher to destabilize a group of military computers with a single attack."
Right. I can't think of a single instance of a vulnerability that affects both Windows and Mac. And Apple have always been proactive and fair when dealing with security researchers, so that's good.
Seriously, though, the real reason Mac's aren't subjected to more drive-by-downloads and malware in general isn't that OS X is significantly more secure than XP or Vista. It's that OS X is still a tiny fraction of the potential pool of malware victims. (An all-time high of 7% as of last month.) It's not worth the money for the botnet czars to develop exploits and bots for OS X. But if somebody really big like, I dunno... the U.S. Army were to deploy Macs in large numbers, then the scale might begin to tip toward profitability.
And then hold on to your blackberry green tea frappuccino, pal. Here it comes.