Have you tried turning off System Restore, booting into Safe Mode and scanning in Safe Mode? That’s what I did.

Also can you look in your Logs and find the pathnames for the infected files? If they’re in your System folder Avast probably won’t be able to deal with them itself but the chaps here might have solutions to help you.

This thing was actually piggybacking itself on top of a .exe file I had saved in My Documents and was giving the file the extension of /setup.exe so I had the .exe file for Ace FTP Freeware calling itself aceftpfree.exe/setup.exe.

I was using the Avast version of 19th October then it updated late last night so I’m going to scan again tonight to be safe.