Link to viruses written for a system that only has .5% of the install base.
Obviously it will depend on what type of virus we are talking about and how big the security hole is. I’m not saying OSX is complete rubbish. It does have decent security; however, it’s not fool proof. Most viruses today require user interaction and for that you will either target an individual that you want to trick or you will target the masses.
Writing such a virus for the Mac obviously isn’t worth the effort (yet) even though we know they exist as proven by the pawn2own contest having OSX being the first one hacked 3 years in a row!
According to Jeff Jones, the director of Microsoft's security group, the Pwn2Own contest is "simplifying security to the point of uselessness."
Pretty much as useless as counting "vulnerabilities" without looking at their practical application, I'd say.
Note that all of the browsers at these events were eventually hacked, and all with pre-developed exploits. That fact that Miller was quicker than his competitors has little to do with the overall system security.
I'll just let you do a search. Here's a few that didn't require any user intervention:
Witty worm, population of around 12,000 installations of ISS security software. Infected all vulnerable hosts in less than an hour. The worm was released the day after a patch was released for the exploit, and most administrators had not yet applied it (a good admin doesn't just patch his enterprise software without testing first).
SQL Slammer, population of maybe a few million installations of MSDE (often installed as part of a third-party software installation) and SQL Server. Infected up to 100,000 hosts within 10 minutes.
The 1998 AutoStart worm spread rapidly through the Mac community even in the age of disk-based transmission. The Mac population was at rock-bottom at this point. The prior year Michael Dell had famously said that Apple should close shop, and the successful iMac wouldn't be released until months later. Apple was at the height of its irrelevance and obscurity, and yet someone bothered to release a successful auto-spreading worm for the platform.
If you want a perfectly secure computer I suggest filling the case with cement and using it as a doorstop. If you want to actually use your computer, then for whatever reason OS X has the better track record of real-world security.