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I am back from the east coast and needless to say, have a lot of things on my mind regarding the whole NSA privacy matter. As a person who has written extensively on this subject for the last several years I confess to a grim satisfaction regarding my worst fears being realized and the way things have shaken out. Hopefully I will have time to put my thoughts together tomorrow. The following is a partial look at an interesting but slightly pointy headed study published in Nature Magazine about how much identity information can be gleaned about the identity of a subject with merely four human data points. Highly technical but I am sure that some of you are smart enough to figure it out if you read the entire study. Then you can explain it to me.

Unique in the Crowd: The privacy bounds of human mobility

Yves-Alexandre de Montjoye, César A. Hidalgo, Michel Verleysen & Vincent D. Blondel

Scientific Reports 3, Article number: 1376 doi:10.1038/srep01376
Received 01 October 2012 Accepted 04 February 2013 Published 25 March 2013

We study fifteen months of human mobility data for one and a half million individuals and find that human mobility traces are highly unique. In fact, in a dataset where the location of an individual is specified hourly, and with a spatial resolution equal to that given by the carrier's antennas, four spatio-temporal points are enough to uniquely identify 95% of the individuals. We coarsen the data spatially and temporally to find a formula for the uniqueness of human mobility traces given their resolution and the available outside information. This formula shows that the uniqueness of mobility traces decays approximately as the 1/10 power of their resolution. Hence, even coarse datasets provide little anonymity. These findings represent fundamental constraints to an individual's privacy and have important implications for the design of frameworks and institutions dedicated to protect the privacy of individuals.

Derived from the Latin Privatus, meaning “withdraw from public life,” the notion of privacy has been foundational to the development of our diverse societies, forming the basis for individuals' rights such as free speech and religious freedom1. Despite its importance, privacy has mainly relied on informal protection mechanisms. For instance, tracking individuals' movements has been historically difficult, making them de-facto private. For centuries, information technologies have challenged these informal protection mechanisms. In 1086, William I of England commissioned the creation of the Doomsday book, a written record of major property holdings in England containing individual information collected for tax and draft purposes2. In the late 19th century, de-facto privacy was similarly threatened by photographs and yellow journalism. This resulted in one of the first publications advocating privacy in the U.S. in which Samuel Warren and Louis Brandeis argued that privacy law must evolve in response to technological changes.

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Modern information technologies such as the Internet and mobile phones, however, magnify the uniqueness of individuals, further enhancing the traditional challenges to privacy. Mobility data is among the most sensitive data currently being collected. Mobility data contains the approximate whereabouts of individuals and can be used to reconstruct individuals' movements across space and time. Individual mobility traces T [Fig. 1A–B] have been used in the past for research purposes and to provide personalized services to users. A list of potentially sensitive professional and personal information that could be inferred about an individual knowing only his mobility trace was published recently by the Electronic Frontier Foundation. These include the movements of a competitor sales force, attendance of a particular church or an individual's presence in a motel or at an abortion clinic...

You also might find the following article interesting at ProPublica; No Warrant, No Problem: How the Government Can Get Your Digital Data