I like Grif's list at http://www.cnet.com/forums/discussions/how-to-remove-pup-option-603542/#post-f742c795-5881-433b-a29b-6d758efe5cd3
Occasionally, my computer becomes slow and unresponsive. I would shut-down the computer and re-start it. As it’s shutting down, near the end of its shut-down cycle, a pop-up window appears asking if I should Abort or Continue a Download that is in Process. I have no idea what the Download is. Having a healthy level of paranoia, I fear the Download might be some kind of malicious spyware or somesuch. Could somebody tell me how to investigate this and find out exactly what this mysterious Download might be?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic