The US National Security Agency (NSA) began collecting Americans’ phone records in 2001, as part of far-reaching surveillance programmes launched by then-President George W. Bush in the aftermath of the 9/11 attacks.
However, the scope of the practice, continued under President Barack Obama, only became apparent in June when ex-CIA contractor Edward Snowden leaked classified US surveillance files.
It emerged that a US secret court had ordered phone company Verizon to hand over to the NSA the phone records of tens of millions of American customers.
This information, known as metadata, includes the numbers of the originating and receiving phone, the call’s duration, time, date and location – for mobiles, determined by which mobile signal towers relayed the call or text.
The contents of the conversation itself, however, are not covered. The surveillance applies to calls placed within the US, and calls between the US and abroad.