Microsoft is evil...but their systems can be secure.
I use *nix exclusively for work that needs to be secure. I would never use Windows for anything other than running a personal computer at home so I can play games. This is my personal preference. But if someone says that an operating system is more secure than another then they are sadly mistaken. Any valid OS, *nix, Doze, etc... are only as secure as the sysadmin make them. Thus, the most secure system has the smartest people working on it. That is why it is harder to break into Microsoft than it is to break into a military base run by 18 year old high school drop outs.