Lee Rigby murder: Should online surveillance be wider?
Technology companies have to do more to flag up terror threats on their websites, Prime Minister David Cameron has said.
The report into Fusilier Lee Rigby's murder found one of his killers spoke online about murdering a soldier five months before the attack.
The intelligence agencies did not know about this exchange, understood to have been on Facebook, until afterwards.
Facebook said it did not allow terrorist content and aimed to stop it.
Security Correspondent Gordon Corera looks at the issue of online surveillance.
25 Nov 2014