Thanks for the sympathy - I know where that is in the Oxford Dictionary
In order:
It was Avast that 'appeared' to have let it through
GG - I did that early on and cannot see anything suspicious - I'm pretty sure it is in the reg, but again Hijack this shows no nasties that I recognise. It's not that I cannot delete the folder - if I change the attributes I can. It just reappears on reboot.