According to many PC magazines that have done research on this subject, they found out that the most powerful software was AVP from Kaspersky lab. They usually win by a big margin when it comes to virus definition data base. I remember a year or so ago, maybe more, when the CIH virus was acting, they were the only ones for a long period of time to be able to detect it and cure the PC.
I was using Norton before, then switched to AVP, and was using it for 1 year (the license expired

). My experience is just great with this, it is absolutely user-friendly and does not end up everywhere like MacAfee does and You can not get rid of it afterwards. This anti-virus program is great with a daily ! virus list update.
You can get it here:
AVP link
Give it a try, it is better than NA in my opinion, and not only in my...