I'm using Active Virus Shield http://www.activevirusshield.com/antivirus/freeav/get_started.adp it's from AOL, yeah yeah I know ;) & it's based on Kaspersky, it's free with daily free updates (if needed) & I hardly ever see the thing except if it finds a bad file & it wants me to decide what to do with it.

Windows 7 64Bit
Poser Pro 2010 SR1