How Ads Follow You from Phone to Desktop to Tablet

One of these recent waves has been greater sophistication of companies engaged in “probabilistic matching,” the study of millions of Web users to determine who is likely to be the same person across devices. For example, Drawbridge, which specializes in matching users across devices, says it has linked 1.2 billion users across 3.6 billion devices—up from 1.5 billion devices just a year ago.
http://www.technologyreview.com/news/538731/how-ads-follow-you-from-phone-to-desktop-to-tablet/