I've just read this piece of new & was quite surprise to find that Vista more secure than mac. anyway here's a snip from the article:
I have found the code quality, at least in terms of security, to be much better overall in Vista than Mac OS X 10.4. It is obvious from observing affected components in security patches that Microsoft’s Security Development Lifecycle (SDL) has resulted in fewer vulnerabilities in newly-written code. I hope that more software vendors follow their lead in developing proactive software security development methodologies.
the whole article can be found here from macworld: