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Ahead of a meeting between David Cameron and Barack Obama, Number 10 are announcing what they say is "an unprecedented level of co-operation" between the USA and UK on preventing cyber-attacks.

Cameron is expected to seek Obama's support for making sites like Twitter and Facebook co-operate more with British intelligence agencies.

Howard Schmidt, who was until 2012 a cyber-security coordinator for the Obama administration, told Today: "We've had a tremendous amount of cooperation between the United Kingdom and the United States."

He said that greater cooperation "will enhance what we've been doing thus far because the threat is much greater."

"There will be less restrictions on exchanging information back and forth, on location of suspects."

First broadcast Today programme 16 January 2015.