Millions of Verizon customers awoke Thursday to learn that the National Security Agency has been secretly collecting their telephone records, under a classified court order granted to the Obama administration in April.

According to a report by The Guardian‘s Glenn Greenwald, the order requires Verizon, one of the nation’s largest telecommunications providers, to give the NSA information on calls from within the U.S., as well as between the U.S. and foreign countries on an “ongoing, daily basis.” That information includes the numbers of both parties on a call, location data and the time and duration of the conversation, according to The Guardian.

The report has brought flashbacks of the highly controversial domestic surveillance program first initiated by the Bush administration in the wake of the 9/11 attacks.

The inside story of that effort was uncovered in 2002 by Mark Klein, a former internet technician with AT&T. In the following clip from the FRONTLINE film Spying On The Home Front, Klein describes how he first pieced together that the NSA was building a massive top-secret data mining operation in a nondescript room just steps from his desk. Eventually, he told FRONTLINE, “it all clicked together to me … ‘Oh, that’s what they’re doing. This is a spy apparatus.'”

A senior Obama administration official defended the program Thursday, telling The New York Times that, “Information of the sort described in the Guardian article has been a critical tool in protecting the nation from terrorist threats to the United States, as it allows counterterrorism personnel to discover whether known or suspected terrorists have been in contact with other persons who may be engaged in terrorist activities, particularly people located inside the United States.”