There's virtually no such thing as a computer that is 100% proof against any malware. And you seem to be running a sensible combination of software.
Except that you haven't mentioned a firewall. Are you running one?
If you;re relying on the built-in Windows firewall, then (depending on which version of Windows) it may not be checking your outgoing traffic - only your incoming.
A good free firewall is Zone Alarm click here