As far as you know.

Well managed and secured Windows 7 is actually probably more secure than any other major desktop OS right now (iOS blows it out of the water of course). OSX is more secure out of the box for a single user deployment perhaps (largely due to being less of a target), but in a corporate environment, it's harder to really lock down OSX than anything else. Sadly.

Indeed. Our security police means that we have to put our iOS and Macs on the DMZ rather than internal network.

Oh believe me, we know.

Famous last words.

Sorry, but a basic principle of security is to assume that you are already 'owned'.

Actually no, that's part of risk assessment i.e reactive security.

A better basic principle is guard all your doors, windows (excuse the pun) and cracks religiously (proactive).