The NSA uses data-mining tools to collect the metadata - the record of communication but not, apparently, the content - of emails, internet searches and telephone calls.
The Guardian newspaper, which broke the story, found the NSA collected 97 billion pieces of intelligence from computer networks worldwide in March this year alone, an unprecedented violation of privacy.
Crucially, the story depended on leaks to the Guardian from Edward Snowden (an ex-CIA technical contractor who volunteered his identity), an avenue the Obama Administration seems bent on closing.
Prosecutors are expected to argue that material leaked by Manning and published by WikiLeaks was found on Osama bin Laden's laptop. But does leaking material mean Manning "knowingly" supplied it to the enemy?
Traditionally, prosecutors must prove intent. Whether this will apply in the Manning trial - which began last week at Fort Meade, Maryland, much of the months-long court martial expected to unfold in private - is unclear.
But the use of the draconian 1917 Espionage Act - originally devised to prosecute, and potentially execute, spies - sends a sobering message. It has profound implications for a free press that holds power to account.
The Manning trial highlights deepening tension between the Administration and the Fourth Estate which has festered during the decade-long "war on terror" and begs the question: where does legitimate national security end and the public's right to know begin?
Last month the Administration's witch-hunt against whistleblowers escalated when Attorney-General Eric Holder admitted the Justice Department [DoJ] had secretly seized two months of phone records from the Associated Press.
Determined to trace the source for a 2012 AP story about a Yemen terror plot, the DoJ secretly tapped 20 AP phone lines of editors and reporters. At no time was AP informed and given a chance to appeal the DoJ move in court.
Holder's claim a "very serious leak" threatened the US did not stem a firestorm of condemnation from Congress, media and civil rights groups, amid dark comparisons with Richard Nixon's presidency, a White House nadir.
The AP case was followed a week later by news of a secret DoJ investigation that seized emails in May 2010 from James Rosen, a Fox News reporter who used a State Department source covering North Korea's nuclear tests.
And on May 28, LulzSec hacktivist Jeremy Hammond pleaded guilty in a New York court to stealing 5.5 million emails - posted on WikiLeaks last year - from private US intelligence firm Stratfor. He faces a 10-year prison term.
Is the Administration going after journalists? Attorney-General Eric Holder is adamant it is not. Holder told Congress he knew of no efforts to use the Espionage Act to prosecute journalists, as this would not be "wise policy". He said "reporters should not be at risk for doing their legal job".
But the DoJ affidavit used to search Rosen's emails, makes the case "there is probable cause the reporter has committed violation [of the Espionage Act] at the very least, either as an aider, abettor and/or co-conspirator."
On May 21, the US-based Committee to Project Journalists [CPJ], which defends foreign journalists from repressive regimes, fired off a letter to Holder saying DoJ actions "undermine press freedom in this country" and set a "terrible example for the rest of the world, where governments routinely justify intervention in the media by citing national security".
The implications of the AP case and the Manning trial - especially the prosecution's rationale that leaks disseminated by the media aid the enemy - are far-reaching.
Holder has used the Espionage Act six times against government whistleblowers, more than any previous administration since 1917. "It's escalated a great deal in terms of the aggressiveness the Administration is using in trying to cut off those leaks," says Sandra Mim Rowe, the CPJ chairwoman who questions its legality.
So, might the DoJ, which hounds foreign hackers or alleged IP pirates like Kim Dotcom, indict foreign reporters?
"One of the interesting things about the Espionage Act is that it's not limited to US citizens," says Shane Kadidal from the Centre for Constitutional Rights. "But what duty or loyalty does someone who is not a US citizen owe to the US Government? The obvious answer is none." If Assange is extradited to the US for trial, this question will be paramount.
A 1972 Supreme Court ruling, Branzberg v Hayes, compels journalists to give evidence in criminal cases. But the court said subpoenas must be narrowly defined and signed off by the Attorney-General. Seizing two months worth of AP material sounds suspiciously like a fishing expedition.
This is a murky area. While the Fourth Amendment protects citizens from illegal search and seizure, the third-party records doctrine asserts government can access data a suspect willingly gives to third parties - such as internet providers who offer "cloud" storage - without a search warrant.
Rowe also points to "a lack of balance between the rights of citizens to full information and the need for government to have national security secrets".
Last year, 4.9 million people held a security clearance, the Office of the Director of National Intelligence said. Any state is obligated to protect national security. But there is concern this national security state feeds off its own momentum and is opposed to transparency. Obama may find his legacy linked to Nixon's if he denies the media's use of leakers to examine actions taken in the public's name.
Famous leakers
*Daniel Ellsberg: A military analyst, he passed the Pentagon Papers - a secret Defence Department study of US involvement in Vietnam - on to the New York Times and other newspapers in 1971.
*W. Mark Felt: An associate director at the FBI, he was Deep Throat, the source who gave information about Watergate to the Washington Post in the 1970s. He unmasked himself in 2005.
*Mordechai Vanunu: He was an Israeli nuclear technician in 1986 when he revealed Israel's nuclear weapons programme. He served 18 years in prison.
*Frederic Whitehurst: Beginning in 1992, the FBI agent exposed shoddy work and inaccurate testimony from the bureau's crime lab.
*Jeffrey Wigand: A Brown & Williamson tobacco executive, he co-operated with CBS television news magazine 60 Minutes and the Food and Drug Administration in the 1990s in exposing cigarette manufacturers' practices. His story was made into the film The Insider.
*Bradley Manning: The US Army private gave a trove of classified military and diplomatic material to WikiLeaks. His court martial is underway.
Edward Snowden
*Age: 29
*Raised: North Carolina, Maryland.
*Background: In 2003 he enlisted in the US Army, but was discharged after breaking both legs in an accident during a Special Forces training programme.
*Intelligence work: He was employed by the NSA as a security guard at one of its covert facilities and then by the CIA, working on IT security. In 2007 he was sent to join a CIA station in Geneva. He left for his first job with a private contractor in 2008 on a military base in Japan at an NSA facility. He worked for contractor Booz Allen Hamilton in Hawaii on a salary of about US$200,000. The Washington Post said he used the code name Verax ("truth teller" in Latin) in dealings with the paper. Two British dissenters in the 17th and 19th centuries, Clement Walker and Henry Dunckley, had used the pseudonym.
*Hong Kong: Snowden finished copying the secret documents he planned to leak to the press, and told his supervisor that he would be away from work for a fortnight. He arrived in Hong Kong on May 21. He says he rarely leaves his hotel room, the door to which he has muffled with pillows to prevent eavesdropping. He also puts a large hood over his head and laptop when typing, to prevent hidden cameras picking out his passwords.
*Booz Allen Hamilton: Both the Bush and Obama administrations have chosen to rely on private contractors like Snowden's employer for much of their intelligence work. The New York Times reported that Booz Allen Hamilton earned US$1.3 billion - 23 per cent of its revenue - from intelligence work in the past financial year.
What has been revealed?
Two things. The first is a huge effort to track hundreds of millions of telephone calls made within the United States every day. While the programme does not actually record what was said, it does tell the Government who made the call and what number they were calling, as well as the duration and the location of the conversation. The programme was disclosed in a leaked court document where the US Government compelled a subsidiary of Verizon, the telephone company, to hand over all of its data for three months. The programme has been renewed on a rolling basis for the past seven years and could be happening for all other major telephone companies. The second programme is a more targeted effort to harvest data on foreigners from online sources. According to the Washington Post and the Guardian, the National Security Agency (NSA) has access to information from Facebook, Google and seven other internet giants. The technology companies deny unfettered access.
- Telegraph Group Ltd
