I am now using Windows 7 64 bits and 4GB of RAM. Which free antivirus give better protection? Avast free Antivirus, AVG antivirus free, Avira free Antivirus, Bitdefender Antivirus Free Edition or Ad-Aware free Antivirus+? Regard to system resources usage. Which free firewall can be combine with one of these antivirus which you have chosen? Comodo Firewall, ZoneAlarm Free Firewall or Privatefirewall?