The top US intelligence official stressed yesterday that a previously undisclosed programme for tapping into internet usage is authorised by Congress, falls under strict supervision of a secret court and cannot intentionally target an American citizen.
Director of National Intelligence James Clapper, trying to quell the scandal over US spying, took the rare step for the second time in three days of declassifying some details of an intelligence programme to respond to media reports about counterterrorism techniques employed by the Government.
"Disclosing information about the specific methods the Government uses to collect communications can obviously give our enemies a 'playbook' of how to avoid detection," he said.
The US Government spying project, Prism, is said to have the ability to monitor individuals' activity on the web in unprecedented detail, both inside and outside the US.
Clapper said the data collection under the programme, unveiled by the Washington Post and the Guardian, was with the approval of the secret Foreign Intelligence Surveillance Act Court and with the knowledge of internet service providers.
He emphasised that the Government does not act unilaterally to obtain that data from the servers of those providers.
The National Security Agency filed a criminal report with the Justice Department last week in relation to the leaks, said Shawn Turner, a spokesman for the Office of the Director of National Intelligence.
President Barack Obama defended the counterterrorism methods on Saturday and said Americans need to "make some choices" in balancing privacy and security. But the President's response and Clapper's public stance underscore the nerve touched by the disclosures and the sensitivity of the Obama Administration to any suggestion of trampling on civil liberties.
The Guardian reported yesterday that it had obtained top-secret documents detailing an NSA tool, called Boundless Informant, that maps the information it collects from computer and telephone networks by country. The paper said the documents show NSA collected almost 3 billion pieces of intelligence from US computer networks over a 30-day period ending in March, which the paper says calls into question NSA statements that it cannot determine how many Americans may be accidentally included in its computer surveillance.
NSA spokesperson Judith Emmel said that "current technology simply does not permit us to positively identify all of the persons or locations associated with a given communication".
She said it may be possible to determine that a communication "traversed a particular path within the internet", but added that "it is harder to know the ultimate source or destination, or more particularly the identity of the person represented by the TO:, FROM: or CC: field of an email address or the abstraction of an IP address."
Emmel said communications are filtered both by automated processes and NSA staff to make sure Americans' privacy is respected.
Britain's Foreign Secretary William Hague will defend British co-operation with foreign intelligence agencies today as he comes under mounting pressure to reveal whether he authorised use of the American spying system.
Political tension over the affair has mounted in Britain, with ministers facing questions over how GCHQ, the British eavesdropping agency, came to use Prism since at least June 2010. Last year it generated 197 intelligence reports based on data harvested through the system.
According to the Guardian, the Prism programme appeared to allow GCHQ to circumvent the formal legal process required to obtain personal material such as emails, photographs and videos from internet companies based outside the UK.
Big Brother is watching
The Patriot Act
In the wake of the terror attacks on New York City and Washington DC, the US Patriot Act of 2001 gave the United Stakes federal Government unprecedented access to telephone and computer exchanges and expanded its right to wiretap. But it also dictated that financial, library, travel, video rental, phone, medical, church, synagogue or mosque records held by third parties can be searched without the public's knowledge or consent as long as the Government says it is acting against terrorism.
The social network, founded in 2004, has prompted hundreds of millions of people to put details of their lives on public display. The company has come under fire for making people's personal photos available for use in advertisements, but media reports suggest the Government has scoured Facebook's servers for audio, video, contacts, e-mails and other documents.
Cellphones with built-in GPS capabilities could allow users to be electronically tracked. As of this year, more than half of all American adults use smartphones.
Remote frequency identification, or RFID, chips
The Department of Agriculture used it to keep track of cattle being medicated, but RFID technology is now in everything from commuter passes to key cards. Tags can be linked on the internet and read without the holder's knowledge or permission.
Loyalty or "rewards" cards
Memberships in such programmes, which offer savings while tracking spending habits, have grown from 973 million in 2000 to 2.7 billion last year.
Automated teller machines, or ATMs
Most often equipped with cameras, there are an estimated 414,000 ATMs in the US, a 28 per cent increase since September 2001.
Automatic licence plate recognition systems
Around since the 1970s, use of the technology has exploded since 9/11, allowing law enforcement to keep tabs on drivers' movements.