Gen. Keith Alexander is director of the National Security Agency, whose duty, his office has said, "requires us to attempt to collect terrorist communications wherever they traverse global infrastructure." Evan Vucci/AP hide caption

itoggle caption Evan Vucci/AP

Say hello to your microbiome, Rob Stein. Our intrepid correspondent decided to get his gut bacteria analyzed. Now he's wondering if he needs to eat more garlic and onions. Morgan Walker/NPR hide caption

itoggle caption Morgan Walker/NPR

Cell towers are constantly tracking the location of mobile phones. And that data, federal courts have ruled, is not constitutionally protected. Steve Greer/iStockphoto.com hide caption

itoggle caption Steve Greer/iStockphoto.com

A promotional image from Renew shows one of its recycling/advertising kiosks in London. City officials asked the company to stop recording data about the phones of passing pedestrians. Renew hide caption

itoggle caption Renew

Value and meaning come from relationships and context. A physical object, such as a quarter, only holds the value we give it. It has no intrinsic worth. iStockphoto.com hide caption

itoggle caption iStockphoto.com

Google, like Facebook, Microsoft and other Internet companies, is concerned that data requests from U.S. surveillance agencies could ultimately damage its reputation in the U.S. and overseas. Justin Sullivan/Getty Images hide caption

itoggle caption Justin Sullivan/Getty Images

Big Data may not be much to look at, but it can be powerful stuff. For instance, this is what the new National Security Agency (NSA) data center in Bluffdale, Utah, looks like. George Frey/Getty Images hide caption

itoggle caption George Frey/Getty Images