Avira Antivir is the best free Anti Virus. Been using it for a couple of years and never a problem, usually an update daily.
Check out AV-Comparatives. An Info Sec friend turned me onto it.
http://www.av-comparatives.org
They perform independent testing of all the major virus scanners on a semi regular basis.
All the other virus scanners mentioned (AVG, AVAST) are OK as well. Avira, McAfee and Symentic are currently the best and have been for a while. Archived reports dating back to 2004 are also available at AV-Comparatives.
Norton use to be bloated, but the new 2009 is slim and fast, wish it was free (legally)
Good luck defending your turf.
I can't wait for the day Ethernet enabled receivers and players need virus scanners...
