Isn't it nigh impossible for a system - any computer system - to be 100% virus free? All they are are algorithms, so finding a hole may be a monumental task but it isn't impossible, and even the U.S military recognizes that someone with no life is perfect for pulling off mad stunts like that (read: taking out somolian pirates).
The reason Macs don't have viruses is because nobody cares enough to code one.
Macs actually do have viruses, but no-one can tell because that's how they always run.
The New Sonic runs best on Mac! (Backwards compatibility not available)
They used to send Macs to disadvantaged African Children but the kids sent them back.
The only thing worse than a Microsoft Windows system is a MAcintosh Apple system.
Steve Jobs is actually a gorilla, and he programmed the first Mac all on his own. His parents were so proud, they went out and bought him 15 bananas right away.
That first one? It isn't a joke... Windows is so virus prone because so many people use it so if you want the most hits, you build for the most popular platform.
Fun fact: Google employees use Apple computers instead of Windows, but why you might ask? Three reasons, firstly because they can still use Java thanks to all the hard work Sun did, nothing that Apple did themselves, secondly due to less viruses because nobody uses apple, and thirdly because less things work on apple, so less likely for employees to play games on their work computer.
No shit, those are the three reasons detailed in their procurement documentation.