once in a while an unwanted IE pop up appears. a short sniffing (using Wireshark) reveals DNS queries such as these:
i have tried using Adaware, Spybot S&D, RemoveIT Pro v4 - SE and Malwarebytes' Anti-Malware. all of them find some infected cookies and fix them, but the problem is not resolved.
after using using DDS i have noticed the entry "Advertising Center" under "Installed Programs". since i suspected it was the reason for the annoying pop ups, i looked it up in the add/remove programs list. it wasn't there. so i used TuneUp Utilities 2009 advanced uninstall feature to remove it. after running DDS again, there is no indication for "Advertising Center" but the behavior remained the same.
waiting for your guidance and thanks in advance for anyone trying to help!