If you are not paying for it, you are the product: How much do advertisers pay for your personal data?

Online advertising is progressively moving towards a programmatic model in which ads are matched to actual interests of individuals collected as they navigate the web. Letting the huge debate around privacy aside, a very important question in this area, for which very little is known, is: How much do advertisers pay for an individualu0027s personal data? In this study, we develop a first of its kind methodology for computing exactly that - the price paid for oneu0027s privacy - and we do that in real time. Our approach is based on tapping on the Real Time Bidding (RTB) protocol to collect cleartext and encrypted prices for winning bids paid by advertisers in order to place targeted ads. Our main technical contribution is a method for tallying winning bids even when they are encrypted. We achieve this by training a model using as ground truth prices obtained by running our own probe ad-campaigns. We implement our methodology through a browser addon and a back-end server that provides it with fresh models for encrypted bids. We validate our methodology using a one year long trace of 1600 mobile users and demonstrate that it can estimate a useru0027s worth with more than 82% accuracy.