As far as changing your virus scanner goes, I suggest AVG and/or Avast antivirus, both are free. (Normally you do not want to run more than one antivirus, but Avast is designed to run as a secondary scanner and I use both programs without a problem.)
Avast isn't designed to be used as a secondary scanner- where did you read that information? It's a full antivirus program, with on access protection.