I use the free version of avast anti virus and have had no problems,(touching wood),I am very happy with it.I once had Norton,but alas my xppro was completely defeated by a virus.Thru much work,malcontent,and try try again,I am up and running using only free and xppro firewall for protection.
In addition to Avast by Alwil Software I am also using AdawareSE which is also free.
If either of these companies were to ask me for a review,I would most happily give them one that they would be proud of!
Well thats all fffolks,happy motoring and the best of luck.
Mike