I use, Zone Alarm, AVG, Ad-aware SE and Spywareblaster, with no problems. And best of all .... they're FREE! Go to this site to find all you need ...... http://www.computeractive.co.uk/downloads/
I use ad-aware se, AVG Free, a-squared, all have free updates. If you get any problems that these cant fix, try Ewidow free trial, you can use it for about 2 weeks free and unlike some free trials , once you remove the viruses they stay removed , even after you stop the free trial.