The Mac has its die-hard fans, but it's never been a mainstream computer. As a result, online criminals have never had much of a reason to pay attention to it. In fact, Mac owners often claim that the lack of Mac viruses are a good reason to buy one of the lovely-looking computers.
However, a recent spurt in the Mac's popularity could have an interesting side-effect, making it a more attractive target to hackers. For more on this see the feature I wrote for MacUser this month.