Macs are still on 0 viruses (that'll do owt) and 0 trojans. People say there have been 23 viruses for macosx but i've never met anyone who's ever known anyone who's seen one. I think 0 is more likely at the moment.
Around 100,000 viruses for windows.
The only real mac exploit involved physical contact with the machine!! usb stick.
Unix is inherently more secure.
The only '5% so why bother' argument is a load of rubbish – it's a huge target, mainly because mac users go round saying they're so secure.