Re: "Im not sure if I can mention it, delete if so, but if you are over worried, then you could always try a scan with other software that can be installed alongside avast, such as malwarebytes."
The avast guy on the phone lectured me that malwarebytes cannot be on the same computer as avast, even if mb is not running or is just a left-over registry key after it is uninstalled, and would cause such a popup malfunction. (It was all about how I had messed up my system somehow to cause this; I think they are trained incorrectly to blame the user?) But that is what he said about mb.