I'm a pretty die hard linux guy, and I think Windows is a bloated nightmare, but it's not insecure IMHO (unless you consider "privacy" to be security, but most people do not (even though I think they should)). There was a time when that wasn't as true, though. If Windows were rewritten from scratch today, I'm certain there would be some different architectural/design decisions made, but that's true for pretty much every piece of software ever written.
