Earlier quoted context omitted.
Oh please. Compared to over a billion PCs worldwide? If you are going to build a bot-net, would you really target the Mac? Gimme a break dude. Considering the vast difference between Windows and OS X APIs; it's quite clear why mal-programmers don't waste their time with OS X. You would have to spend MORE than half your time attacking the Mac for less than 10% of your total attack surface. The only other argument that…
So by that logic, as long as the Mac market share isn't as high as Windows market share, the Mac platform will always be safer.
iOS might be another story, but smartphone and tablet usage in general is still dwarfed by Windows usage. Despite that, within the realm of smartphones there have been more iOS threats than there have been threats for Windows Phone 7. Shocker? Nope. It's based on popularity.
Interestingly enough, this year's Pwn2Own left the Android and Windows Phone 7 devices undefeated while the iPhone was one of the first to fall. - http://www.wired.com/gadgetlab/2011/03/hacking-android-windo...
Take from that what you will. Ciao.