Well, here's the freaky part: After having tried other alternatives (Anti virus software etc.) I formatted my hard drive and reinstalled Windows XP. Increadibly enough, the problem remained. No internet connection but still fake windows pop-ups. I have tried WinSock with no luck, as well as almost any spyware/antivirus product out there (although I can't update any program since I haven't got direct internet access).
What can I do? Any ideas?