AVG free edition is what I used to use, and then later the pro version or whatever it's called. I thought it was great, until I tried another scanner and found 2 or 3 viruses sitting on my pc :/
I ran Kaspersky for a while and in my experience (of fixing everyone else's computers) it's the best at system scanning (around 99% of all viruses will be caught). However I prefer NOD32, which also had a good system scan but also a fantastic real time protection system that basically stops me getting any viruses sneaking in in the first place, on websites...anywhere really, terminating self downloaders. Saves me hassle as I'm lazy
![Wink ;)](./images/smilies/icon_wink.gif)
Either NOD32 or Kaspersky is best
I think they only have trials rather than free editions though. Depending on your definition of "free". Ahem. What I recommended to people using one of the cheaper or free virus scanners (or rubbish ones like norton or mcafee) is if you really can't get a non-free scanner then the least you can do is run AVG free alongside another virus scanner. Between them they should catch most viruses although it's still not as good as getting a better scanner in the first place. If you are doing that though, periodically download the latest version of stinger from this website:
http://vil.nai.com/vil/stinger/ It's a program that specialises in many of the nasty trojans and worms that many pcs are susceptible too, both common and rare. I use it on other people's pcs a lot