Of the free AV programs, Avast and Avira both consistently hit the highest scores in virus detection tests. In fact both are usually in the top 5 of ALL A/V programs with detections rates of 95% or above
Of the two, Avast has a wider range of abilities, which is why it gets my vote. Its what I install on any machines I have to clean up for customers - and so far I've never had one come back to me infected. However I use it as part of a cocktail of free software - which all work together OK without clashing
Avast Antivirus free (version 7 released this week)
Threatfire - a behavioral scanner with a very good hit rate for rootkits zero-day attackes
Windows Defender - already installed on Vista / &, optional download on XP
Browser Protect (
Browser Hijack Protection for free - BrowserProtect.org) - stops browser hijacks
Spamfighter (if sing a POP/IMAP mail client)
I don't bother with additional firewalls unless a customer demands it, in which case I use Zonealarm. My experience is that for most people the firewall built into Windows from XPsp3 onwards works well enough. Installing a 3rd party firewall requires too much intervention for most users and they end up turning it off
if you have really nasty browsing habits, then installing Spybot S&D and Spyware Blaster helps - but only as long as they are kept up to date (a manual process)
I fond it more constructive to use Mozilla Firefox and then lock it down with security plugins - if you can protect the browser, generally you can protect the computer