30-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.
Timeline: How US surveillance secrets were laid bare
June 5: British newspaper The Guardian reveals the existence of a secret US court order forcing US telephone company Verizon to provide the National Security Agency with daily information on its customers' calls from April to July this year.
June 6: The Washington Post and The Guardian report that the NSA and the FBI have access to the servers of major internet companies such as Microsoft, Yahoo, Google and Facebook in order to monitor the web traffic of people outside the United States. The programme, called Prism and in effect since 2007, stems from a law approved under the presidency of George W. Bush and renewed in December 2012. The internet companies deny they have given the government backdoor access to their servers.
June 7: US President Barack Obama says America has to find a balance between privacy and security.
June 9: As US authorities announce they have started an investigation, Snowden, who has been in hiding in Hong Kong since May 20, reveals himself to be the source of the leak in an interview with The Guardian.
June 10: Snowden leaves the Hong Kong hotel where he had been staying, but his exact whereabouts are unknown. Some US lawmakers call for his extradition.
June 11: The American Civil Liberties Union files a lawsuit against the "unconstitutional" telephone record collecting programme.
June 12: The European Union toughens its tone with the United States and asks for clarifications regarding Prism. NSA director Keith Alexander says the programmes were approved by the court system and Congress. Snowden resurfaces and tells the South China Morning Post he wants to stay in Hong Kong, and that the US monitors hundreds of thousands of computers around the world, including Hong Kong and the mainland.
June 13: FBI director Robert Mueller confirms a criminal investigation is under way against Snowden and claims snooping programmes are essential in the "fight against terrorism".
June 15: Facebook and Microsoft reveal that, in the second half of 2012, they received thousands of requests from US authorities for information about their customers - 6,000 to 7,000 in the case of Microsoft and between 9,000 and 10,000 for Facebook.
Monday: Apple says it received between 4,000 and 5,000 requests for information from December 2012 to May 2013. The next day Yahoo says it had 12,000 to 13,000.
Tuesday: The NSA director claims the surveillance programmes helped thwart more than 50 potential "terrorist" attacks since the September 11 attacks of 2001.
Friday: Snowden is charged with espionage by US authorities, who ask Hong Kong to arrest him. A day earlier, a businessman linked to WikiLeaks says people in Iceland are preparing a flight for Snowden so that he can find asylum there.
Saturday: The Guardian, quoting documents released by Snowden, says as of last year, Britain's electronic eavesdropping agency was handling 600 million "telephone events" a day. Snowden is quoted as saying Britain is worse than the US when it comes to such snooping. The Post reports Snowden's claims that the US has hacked fibre-optic cable operator Pacnet and the mainland's Tsinghua University.
Yesterday: Snowden arrives in Moscow on a flight from Hong Kong.