They crowdsourced the data using an Android application and conducted an analysis of individual calls made by the volunteers to sensitive numbers, connecting the patterns of calls to emphasize the detail available in telephone metadata, Mayer said.

"A pattern of calls will, of course, reveal more than individual call records," he said. "In our analysis, we identified a number of patterns that were highly indicative of sensitive activities or traits."

For example, one participant called several local neurology groups, a specialty pharmacy, a rare-condition management service, and a pharmaceutical hotline used for multiple sclerosis.

Another contacted a home improvement store, locksmiths, a hydroponics dealer and a head shop.

'Unambiguously sensitive'The researchers initially shared the same hypothesis as their computer science colleagues, Mayer said. They did not anticipate finding much evidence one way or the other.

"We were wrong. Phone metadata is unambiguously sensitive, even over a small sample and short time window. We were able to infer medical conditions, firearm ownership and more, using solely phone metadata," he said.

All three branches of the federal government are now considering curbs on access to telephone metadata, Mayer noted. Consumer privacy concerns are also salient as the Federal Communications Commission assesses telecom data sharing practices, he added.

Remind me are they trying to demonstrate the danger of the NSA or the danger of Facebook / WhatsApp?