http://www.cnn.com/2004/TECH/internet/04/09/apple.trojan/index.html?iref=newssearch
http://www.cnn.com/2006/TECH/ptech/10/20/apple.virus/index.html?iref=newssearch
don't get me wrong its a much tighter system than windows, but to think your computer is invincible, well thats just ignorance, the only way to make sure you get no viruses or spyware or anything is to not have your computer hooked up to the internet, a totally closed system would be invincible... but whats the fun in that??
The problem is, the first is an trojan. It's not a virus, and you need to actually download the file and execute it to load. They aren't in the same category as virus. The second, was a report that some new iPod were shipping with a WINDOWS virus, which was doing nothing to Mac OS X.