ExtremeTech decided to take a look at how effective Windows Vista's UAC is to keep viruses away from your system.
Vista is full of anti-malware features, and one of the most powerful is User Account Control. The controversial routine blasts users with a confirmation request virtually any time they try to run a program that might alter the state of the system. Vista users, you've seen it: when you try to install a program, to launch Device Manager, or run something as Administrator, the screen goes dark, the system plays an alert noise, and a dialog appears asking for permission to proceed.
While many users consider UAC an annoyance, it could be a godsend in the fight to keep computers malware-free. Viruses, Trojans, worms, and spyware often comes in the form of email attachments, and while knowledgeable users know not to launch executables that come in via email from unknown sources, plenty of less security savvy users get tricked every day.
You can check it out over here. They conclude that UAC is a pretty good protection against malware but that an anti-virus program, or even more importantly a good education and common sense, is still necessary.