According to the technology risk management company mi2g Ltd., Mac OS is one of the most secure OSes out. It had fewer than 25 vulnerabilities, while Windows had well over 500! Linux also had over 200 vulnerabilities. Two other Unix variants shared top honors with the Mac, Sco Unix and Compaq’s Tru64.
MacCentral also has an article on this. I am wondering if this includes OS X as well?