In an Article named by The four columns of security for a safe online experience , SpyBot team recommended Avira Anti-Vir as only one recommended free anti-virus software.

I'd like another software to be added. I consider it very good, it have mail scanner and free. It is Avast Home Edition. Personally, I used to run it with SpyBot and there are no any problems or conflicts. I'm waiting SpyBot team's member to reply and tell me the team's opinion about Avast.