The National Security Agency gathers intelligence to keep America safe. But leaked documents reveal the NSA's dark side — and show an agency intent on exploiting the digital revolution to the full.

U.S. President Barack Obama hailed United Nations Secretary-General Ban Ki-moon as a "good friend" after the two had sat down at the White House in April to discuss the issues of the day: Syria and alleged chemical weapons attacks, North Korea, Israel-Palestine and climate change. But long before Ban's limousine had even passed through the White House gates for the meeting, the U.S. government knew what the secretary-general was going to talk about, courtesy of the world's biggest eavesdropping organization, the NSA.

One NSA document — leaked to The Guardian by whistle-blower Edward Snowden just a month after the meeting and reported in partnership with The New York Times — boasts how the spy agency had gained "access to U.N. secretary-general talking points prior to meeting with POTUS (president of the United States)." The White House declined to comment on whether Obama had read the talking points in advance of the meeting.