Avira AntiVir is the most thorough free antivirus on the market.Without being a resource hog and utilising very little resources,it provides excellent protection from all types of malware.The detection rate is awesome.......99%......moreover it has a very easy to use interface and updates itself automatically.......it also has a scheduler to create tasks and the advanced heuristic engine has proven itself to catch about 60% of new threats..........only the downside is it displays a nag screen while updating...........believe me........you wont regret using this one....