Ok, Naat, before I get into the steps you recommend:

  1. There are no visible issues with my pc now
  2. I just want to clean it up after I unfortuntely downloaded this Trojan
  3. As I said it was just 10 minutes before all over the media appeared warning: do not even touch the mail - the attachment is pretty nasty
  4. I was surprised that avast! did not give me any warning
  5. I ran a scan with avast! afterwords and avast! moved the threat to the chest
  6. After restart there were 2 new issues, avast! moved them to the chest again

I am not exactly sure this means everything is fine and clean. That is why I came here for help…