I'm using Avast too, with the same issue (the sotfware moves the exe file to the trunk of viruses).
But there is a simple way to avoid this in few seconds:
- Place the mouse over the Avast icon in the taskbar.
- Choose the option "Control of Avast shields".
- Finally choose "Disable until the computer is restarted".
Of course, that way you remain unprotected if you use an internet navigator.