I DON'T SEE HOW WE CAN PREVENT THIS

Big Data is certainly a threat to our privacy but so is "little data."  I recall reading about this study and just thought of it as another factoid about human predictability:

Unique in the Crowd: The privacy bounds of human mobility

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

NATURE, Scientific Reports 3, Article number:1376
doi:10.1038/srep01376

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.

If the above link is broken, here's one to the MIT press release and one to a NYT article.