@ Anon. You weren't paying attention.
Macs do have potential security vulnerabilities like every platform. It's just that not many get to be beyond the purely potential. Apple have NEVER said their computers are invulnerable or without flaws, only a few idiotic zealots have propagated that notion. You find idiotic zealots on all platforms.
The fact remains that compared with Windows, for example, Macs are less likely to get into bother. How long this will remain the case will remain to be seen. There have been numerous warnings but few real alarms of any substance.
I have however, taken on board the experience of Windows users, and practice safe browsing, run ClamX AV - mainly to prevent me passing stuff on to Windows colleagues - and run on a non-admin account with Mac OS X. I wish others would do the same and just shut up. It is possible to be a Mac user and only a teensy-weensy tiny bit smug. :•)


