Facebook Promises Encrypted Messaging, but You Don't Need to Wait

"Metadata is valuable because it can be just as revealing as what you write in a message, says Jonathan Mayer, assistant professor of computer science and public affairs at Princeton University in New Jersey, and former chief technologist for the Federal Communications Commission’s Enforcement Bureau.

“The inferences are pretty precise,” Mayer says. In his research, metadata was used to accurately conclude whether text subjects were preparing for medical procedures or using drugs illegally. It could also determine their religious affiliations. Further, because some companies and organizations have dedicated phone numbers for automated services, texting metadata could also reveal which bank and pharmacy you use, and which political groups you support, he says."