AVG vs MS Security Essentials

Is there an antivirus that can do a scan while the computer is off??

There are priority levels for AVG. Do you have it set to lowest, while you’re on the computer doing other things? It is a switch called “Fast scan” at one end and “Slow scan” at the other. You want slow scan. It takes much longer with a slow scan.

Yep - even with Fast Scan everything else slows down and the scan can take a couple hours.

Well, I reinstalled Avira after deleting all other scan programs. It installed fine and is running at the moment. It didn’t function well last time I tried the upgrade, but now it is fine. AVG and MSE are not so good in my estimation. MSE is OK, but Avira is best.