See, I've never understood that argument. Surely all the hype behind Macs not having viruses ensures that no Mac owner installs a virus scanner, therefore these millions of 'unprotected' Macs would be a 'good' target. Millions of baffled users unsure why their Mac has gone tits-up... It can't be a virus, Macs don't get viruses!
I'd imagine it just comes down to OS X being a lot more secure than Windows, I assume, to a degree, this is down to it being based on BSD.
Oh yeah?
http://www.engadget.com/2007/04/22/safari-browser-exploit-produced-within-9-hours-in-hacking-compet/
http://www.engadget.com/2008/03/27/pwn-2-own-over-macbook-air-gets-seized-in-2-minutes-flat/