“Privacy protections against government surveillance are often scoped to communications content and exclude communications metadata. In the United States, the National Security Agency operated a particularly controversial program, collecting bulk telephone metadata nationwide. We investigate the privacy properties of telephone metadata to assess the impact of policies that distinguish between content and metadata. We find that telephone metadata is densely interconnected, can trivially be reidentified, enables automated location and relationship inferences, and can be used to determine highly sensitive traits.

• Evaluating the privacy properties of telephone metadata. Jonathan Mayer, Patrick Mutchler, and John C. Mitchel. Edited by Cynthia Dwork, Microsoft Research Silicon Valley, Mountain View, CA, and approved March 1, 2016 (received for review April 27, 2015. vol. 113 no. 20. doi: 10.1073/pnas.1508081113