The head of the U.S. National Security Agency, Admiral Michael Rogers, said China and "one or two" other countries have the ability to launch a cyber attack on the U.S. power grid and other vital infrastructure.
Rogers, who is head of the U.S. Cyber Command, did not name the other countries because, he said, it is classified information.
But he told a congressional hearing Tuesday that America's enemies are carrying out "reconnaissance" missions to discover how these networks function -- those that operate electrical systems, chemical plants, water treatment facilities, and other critical infrastructure.
Rogers said it is a matter of when something dramatic will happen, not if.
He said the Obama administration is looking at what kind of a cyber-attack would be considered an act of war.