Double click is the Google 3rd party spyware conspiracy.
"Google uses the DoubleClick DART cookie on our Google content network ..."
These guys are the used car salesman of the internet, very 'slippery' characters burying their methods, details & opt out choices with layer after layer, page after page of non-sense & merry-go-round tactics plus non-functioning links, etc.
DoubleClick Ad Exchange is a real-time marketplace partnered with the Google Display Network for buying and selling advertising. It represents another market for advertisers to bid on display advertising across the Internet. When you have a campaign that targets the Display Network, you automatically have access to Ad Exchange publisher sites that comply with AdWords' guidelines.