Every year there is a contest called Pwn 2 Own were hackers get the opportunity to hack Windows, Linux, and OS X operating systems though either Safari, Firefox, IE 7, IE 8, or Chrome. If a hacker does manage to hack into a computer then he gets to keep the laptop he cracked, and $5,000 per browser bug that is exploited. Last year a hacker named Charlie Miller cracked Safari and OS X in under 10 minutes, and this year he managed to do it again. Only this time he cracked the Mac in under 10 seconds and had full control of the computer in 2 minutes. During the first day OS X was hacked a total of three times, while Windows, or comparisons sake, was hacked once. Proof that what I am saying is true, not that I could make it up. Although, I have been told that I'm a great lier, which doesn't make sense because if I was a great lier then how would anyone know if I was lying...?
Of course they are, but why would you bother. There are millions more Windows machines in the world, and Linux/Unix is used to hold a lot of important information, especially historically. Of course hackers are going to target information of value, and not some Mac user's "Home Movies" that he made. I used to hear people say that Mac's were secure or unhackable, which to me meant that the didn't know much about computers or technology.