The Pentagon has created a specialist online unit to counter cyber attack. The newly promoted four-star general, Keith Alexander, takes charge of the Pentagon's ambitious and controversial new Cyber Command.

The big idea that it will he will create a unit that is designed to conduct virtual combat across the world's computer networks. It will mean a change of tactics for the Americans which have for years worked on the basis of developing systems that involve flinging as many bullets or bombs at the enemy until they give up. Alexander was appointed on Friday afternoon in a low-key ceremony at Fort Meade, in Maryland.

The creation of America's most senior cyber warrior comes just days after the US air force disclosed that some 30,000 of its troops had been re-assigned from technical support "to the frontlines of cyber warfare". Cyber Command is being set up as the military is starting to get edgy about how vulnerable it is to a cyber attack.

James Miller, the deputy under-secretary of defence for policy, has hinted that the US might consider a conventional military response to certain kinds of online attack.