I'm using the free version of Treatfire, the Antivirus used is Pc Tools anti virus and not really worth it, says Pc Mag (not that i trust them now, but that's how i found out about it). The free version updates silently too. I don't notice it running, and they're fixing one application incompatibility I reported for the next release.
PC Tools' ThreatFire 3 blocks malware (including zero-day threats) by analyzing program behavior, and it does a better job than many signature-based products. Add its free protection to your security arsenal, but don't pay extra for the less-effective scan-and-clean Pro edition.(http://www.pcmag.com/arti...2C2704%2C2191333%2C00.asp
I have actively settled on Avira AntiVir PersonalEdition Premium ( I got one copy free by using Trial Pay on some photopaper for my inkjet for Â£2.50 - and bought another copy for the other pc) because it comes out very well on tests, I liked it footprint and lack of performance impact and felt dirty setting a local policy to block the popup from appearing.
I'm completely satisfied by it: not had any false positives and you can enable/disable set what things to scan for - from archives to diallers to jokes, on read/write or just read etc).
I just use gmail for my email needs and all spam / viruses get moved out of my inbox (it now also scans mail on the gmail server) - but I suspect either AntiVir or threatfire would notice if something slipped past? Didn't realize the free version didn't scan mail though, good I upgraded, it's only $20 - or use trialpay.