Perhaps a coincidence, but this AdWeek report[1] flags a number of "ghost sites" that offer huge volume of impressions for sale on the exchanges and have real advertisers but don't seem to have any actual human beings present. One site in particular they mention usbuildingdigest.com has a very large number of DSP and other data integrations[2]. Suggestive to say the least. A number of other sites are mentioned in the AdWeek report.

[1] http://www.adweek.com/news/technology/meet-most-suspect-publ... [2] http://imgur.com/WHxmmHo