you always need something more apart from your antivirus even if that antivirus is Avast internet security..no antivirus can guarantee 100% safety.that's why we use these freeware "babies" such as ad-aware,superantispyware,mbam etc..i couldnt agree more with tech and yokenny about MBAM(Malwarebytes anti-malware)..ad-aware isnt as good as it used to be so i wouldnt trust it..as for windows defender i update it but i keep it deactivated because i dont want it to get in the way of avast and steal its "meal"..also i want to keep my system the lightest possible..but having it updated and scanning from time to time wont hurt.