Avast doesnt find virus - yul.exe *32

when i try to launch web browser or file folder, avast detects virus and asks if i want to open application in sandbox-must say ok in order for application to run.

task manager reports that yul.exe *32 is running.
(c:/user/…/appdata/local) but no such file in the directory-have show all hidden files turned on.

I ran full scan using avast but it didnt ID an threats.

any advice on removing this much appreciated.