The US government is worried about "the enemy within." The 9/11 attackers were able to communicate with each other and to undertake their pre-attack activities without the US government stopping them. Not that they weren't detected. Suspicious activity was reported locally by the FBI, but the information didn't trigger any alarms. The Boston bombers and other home grown attackers have been able to access jihadist material through the internet. People who are liable to radicalisation tend to visit known web-sites. Prism is one way of enabling US government agencies to detect the enemy within. Nick Watts, Deputy Director General of the U K Defence Forum, puts the current furore into context.











