According to a test that was made by Sophos about running Windows 7 on a clean system, the operating system is vulnerable with malware.
Sophos said, “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.”
The UAC only blocked one sample.
Chester Wisniewski of Sophos concludes that Windows 7 users still need an anti-virus software for their OS.
Source: The Tech Herald