Edward Snowden

31-year-old American Edward Snowden, a contract employee at the National Security Agency, is the whistleblower behind significant revelations that surfaced in June 2013 about the US government's top secret, extensive domestic surveillance programmes. Snowden flew to Hong Kong from Hawaii in May 2013, and supplied confidential US government documents to media outlets including the Guardian

US Director of National Intelligence James Clapper listens to a senator's question at Thursday's hearing on Capitol Hill. Photo: AP

NSA declines to confirm it tracks movements via cell phone signals

The top US intelligence official has sidestepped questions from a senator about whether the National Security Agency has used Americans' mobile phone signals to collect information on their whereabouts that would allow tracking of the movements of individual callers.