Data held on 'trillions of emails'

Edward Snowden, the rogue NSA contractor who leaked top secret documents to the media. Photo / AP

Information on trillions of emails, web chats and Skype conversations carried out by Americans has been harvested along with their phone records by the National Security Agency, it has been claimed.

The NSA's surveillance programmes, which have been exposed in a series of recent leaks, are now said to be so wide-ranging that they are reported to "touch nearly every American household in some way".

A top-secret court order published this month disclosed that for seven years, US telecommunications corporations are ordered to hand over details of all calls made on their networks.

This vast amount of "metadata", comprising details such as call location and duration, can then be mined by US intelligence to identify associates and potential co-plotters of suspected terrorists.

This programme, code-named "Mainway", has a sister scheme called "Marina" that vacuums up data on trillions of other communications, such as emails and video calls, the Washington Post reported.

Mike Rogers, the chairman of the House intelligence committee, said the spying apparatus had thwarted "dozens" of terrorist plots, details of which he was working to declassify.

The Michigan Republican told CNN that the system was a "lockbox" containing "only phone numbers", rather than recordings. He said it was used "sparingly" and "absolutely overseen by the legislature".

Edward Snowden, the rogue NSA contractor who leaked top secret documents to the media, claimed that even as a low-ranking official he could tap the phones of any American.

Yet intelligence chiefs insist the content of conversations can only be obtained in extraordinary circumstances and with court authority, on the basis of specific evidence of a terrorist plot.

Then, a system called Nucleon records calls, while Prism, which was exposed in documents leaked by Snowden, captures emails, social network messages and other online chats.

William Binney, a former NSA technical director who helped create the agency's eavesdropping network, estimated last week that it records the calls of up to a million people on a "target list".