A DigitalPoint Forum thread discusses one site owner who has mysteriously received two hours worth of free Google AdWords traffic. He received an extra 800 unique visitors from pagead2.googlesyndication.com, the referring source of Google AdWords. The site owner does not have any active AdWords campaigns running. The site owner does not run any affiliate program.
Possible reasons for the traffic listed in the forum?
(1) Spyware or something that changes the referral source of a fake click bot or something similar.
(2) A mistake by another advertiser, where the advertiser plugged in the wrong URL and let it run four two hours before realizing.
(3) A secret admirer who sponsored 800 visitors for this site. :)
Forum discussion at DigitalPoint Forums.