It's actually quite difficult to determine - for real - if updates are available for a Windows box. Many viruses and trojans pull tricks to prevent the Windows update service from working properly, so one might determine that there are no updates when there really are.
We can at least try to ask Windows Security Centre whether or not they have anti-virus, updates, etc. Even if it doesn't provide the correct answer (i.e. it lies because they already have a virus) wouldn't that be better than nothing?
I think we can query Windows Security Centre for Updates, Firewall, and Anti-virus, although I could be wrong as I know very little on the subject.
I'm not sure it's such a good idea to weigh down the official Bitcoin client with what would essentially be a large chunk of anti-malware code.
Would make a good fork though. Alt-client: "Secure bitcoin"