To have done with the pentagon

Al-Qaeda learned from the 2001 attack on the World Trade Center that it had also inadvertently destroyed two key communication switches in the base of the building and had managed to put the New York Stock Exchange offline.

This would mean future attacks were likely to be co-ordinated - combining a physical attack with disabling the electronic infrastructure, he says.

"A simultaneous cyber-attack will inhibit the government's chance to respond," agrees Mr Rasch. "You blow up a building in San Francisco and you take out the phone system or the traffic lights at the same time."