yeah i was happy with avast when i installed 2 years ago, until i got infected, though now i dont know if im infected or windows crashed..
Reading your post it seems to me that you're not infected by a virus, but by a spyware
Gero, if you take a look to my signature you may find some security programs that may help you, in fact as I read in a security site, at least have three or more antispyware programs, in fact today Sunday I scanned my PC with AVG Antispyware and found a trojan.
All the programs are free, so if may take a look at them , maybe it helps you, so I suggest you to download them and tested them
Kindly regards
MiguelAngelXP