Defense One : “A top-secret surveillance program housed at the National Security Agency allows agents to listen in to the entirety of an unnamed foreign country’s telephone conversations that have taken place within the past month, including those for people not suspected of any wrongdoing, according to new documents from Edward Snowden published Tuesday.”  

“The program, known as MYSTIC, was formed in 2009 and deploys a ‘retrospective retrieval’ tool that allows agents to rewind and play back phone conversations that occurred in the past 30 days, according to a new report in The Washington Post . One official described this RETRO tool—for ‘retrospective retrieval’—as a ‘time machine’ that opens a door ‘into the past,’ allowing a replay of the voices on any given call, without the need for prior identification of the person on the line.”