Removal is easy if you attack it in the right order.
1. Install Process Explorer and run it
2. See the PrevAdKeep Tree? Kill the entire tree for it… don’t try kill the PrevAdServe task only or it will keep relaunching.
3. Now permanently delete the directory C:\Program Files\Preview AdService\ files included
THAT’s IT! The key is shutting the bastard off first so you can manually delete the files. This is way easier than rebooting in safe mode.
PS: I highly recommend you install Microsoft’s new anti-spyware tool as well as Spyware Doctor.
See original Mefi thread here: