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Nobody cares about OS X (very small market share), that's why nobody writes virus for it
As a matter of fact is not so hard to write one.

1) Find those buffer overflows in image handling libraries before Apple
http://secunia.com/advisories/36701/
2) Find a privilege escalation bug before Apple
http://www.macworld.com/article/134165/2008/06/ardagent.html
3) Generate images containing the virus (wallpapers, banners, etc) and upload them to as many sites, torrents, etc. as you can
4) The virus should be very quiet and infect newly created images and one of the default system processes
5) Profit!
 
Check the last three words of my post again.

Usually the correct thing to do when you're wrong is apologise. Or at least to stop digging the hole deeper. Just thought you'd want to remember that for future reference.
 
My NEW theory.

I reckon that people who own a mac, are of a higher class (because of their cost) and they belong to the sort of people who DON'T want to ruin other peoples computers / weekends / lives, and you have to own a mac to write for mac (because of the differences between mac and windows).
 
Its too hard to!

There is virus beating software within mac OS X, which stop programmes exploiting it.

It is an extremely secure OS, and, as there have been a few threats in the past, Apple release security fixes often.
 
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