The US National Security Agency (NSA) is capable of collecting and storing almost 200 million text messages a day from around the world, say reports based on leaked documents.
The database of text messages collected in operation "Dishfire" enables the NSA to extract data on people’s travel plans, contact networks and financial transactions.
The documents reveal the UK spy agency GCHQ has made use of the NSA database, in use until at least late 2012, to search the metadata of “untargeted and unwarranted” communications of UK citizens.
But the NSA told the BBC that Dishfire stored "lawfully collected SMS data" and denied that the agency’s collection of data is arbitrary and unconstrained.
In a statement, GCHQ said all of its work is carried out in “accordance with the strict legal and policy framework which ensures that our activities are authorised, necessary and proportionate and that there is rigorous oversight."
The NSA also said its activities were "focused and specifically deployed against - and only against - valid foreign intelligence targets in response to intelligence requirements."
The NSA said text data of US residents may be "incidentally collected", but "privacy protections for US persons exist across the entire process.
"In addition, NSA actively works to remove extraneous data, to include that of innocent foreign citizens, as early as possible in the process.”
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- NSA analysed UK data in secret deal, says Snowden
- NSA and GCHQ unlock online privacy encryption
- NSA and GCHQ mass surveillance violates EU law, study finds
- US publishes revealing review on NSA surveillance
On 17 January, US President Barack Obama is set to announce changes to the US electronic surveillance programmes, based in part on a review of NSA activities by a White House panel.
The White House said Prime Minister David Cameron had been briefed on the review.
An alliance of US technology firms has called for reforms, claiming that some of the techniques developed by the NSA undermine global confidence in US products, including cloud services.
The firms are concerned that public loss of trust in technology will hurt their businesses, and are calling on governments to help restore that trust.
Obama is expected to support the creation of a public advocate to argue in front of the Foreign Intelligence Surveillance Court, a secretive bench that approves the bulk records collections, according to details leaked to US media by the White House.
He is also expected to extend some privacy protections to foreigners, including more oversight on how the US monitors foreign leaders, and limit how long phone information is kept.
But, according to the BBC, Obama is not expected to take the mass collection of phone data out of the hands of the NSA, as the panel recommended, instead leaving that question to Congress.