I found the piece of adware - turns out it was made in some automation software and was designed too simply to be detected by Spybot et al.
I'll mark the best answer below, but it didn't help. I noticed a suspicious 'adobeflash.exe' process running, then found out it was written in .Net 2.0. Yeah, that's really legit.
I seem to have picked up a piece of adware, so I'm trying to trace it down.
All of the running processes seem to have legitimate comments and names, so it'd take too long to try and drill down there - if it doesn't run in a scheduled manner anyway.
How can I trace which processes open webpages on my computer?
(Btw, SpybotS&D only found tracking cookies)