Security researchers from Sophos investigated how well Windows 7 is protected against viruses. Fortunately for security firms like Sophos the new operating system from Microsoft is still quite vulnerable, the researchers found that Windows 7 only blocked two out of the ten viruses they let loose on the operating system. More details over here.
We grabbed the next 10 unique samples that arrived in the SophosLabs feed to see how well the newer, more secure version of Windows and UAC held up. Unfortunately, despite Microsoft's claims, Windows 7 disappointed just like earlier versions of Windows. The good news is that, of the freshest 10 samples that arrived, 2 would not operate correctly under Windows 7.
User Account Control did block one sample; however, its failure to block anything else just reinforces my warning prior to the Windows 7 launch that UAC's default configuration is not effective at protecting a PC from modern malware.
Lesson learned? You still need to run anti-virus on Windows 7.