Both Avast and G Data are excellent standalone programs. G Data has two engines -- Avast and BitDefender -- designed by G Data to work well together. G Data was also the first company to develop an antivirus program. The new Avast also has a compatibility mode for the purpose of allowing it to work with another Antivirus program without any conflicts. I have only tried Avast in the Compatibility Mode with Microsoft Security Essentials and Trend Micro Titanium Internet Security, and they work very well together. Trend Micro Titanium I/S has a firewall booster that can be activated to support and strengthen the Windows Firewall. Other good standalone programs are AVG, Avira Antivir, Panda Cloud, Norton, and BitDefender. The first...