As the amount of data expands exponentially, nearly all of it carries someone’s digital fingerprints. […]
Such data sets are often portrayed as having been “anonymized” in some way, but the more data they involve, the less likely that is to be actually true. Mobile-phone companies, for instance, record users’ locations, strip out the phone numbers, and sell aggregate data sets to merchants or others interested in people’s movements (see “How Wireless Carriers Are Monetizing Your Movements”). MIT researchers Yves-Alexandre de Montjoye and César A. Hidalgo have shown that even when such location data is anonymous, just four different data points about a phone’s position can usually link the phone to a unique person. […]
http://www.technologyreview.com/news/514351/has-big-data-made-anonymity-impossible/