Hi Duncan, welcome to the forum
I just typed out a reply suggesting the possibility of avast! being installed, and saw the 4 was missing...
First off, let me say that I am not completely sure, this is merely a suggestion.
Now this is interesting...
avast! scans data in the _avast4_\unp*.tmp folder <-- notice the 4?
This is very odd to me, can you be certain that it didn't have the 4?
I would suggest i you haven't already got it, to try a scan with MalwareBytes AntiMalware, like one or our resident experts suggests:
http://forum.avast.com/index.php?topic=53253.0-Scott-
EDIT:
And now I just noticed in the title there is a 4...
Are there any avast! processes running?
Can you find the ALWIL Software folder?
C:\Program Files\Alwil Software\