China and "one or two" other countries are capable of mounting cyber attacks that would shut down the electric grid and other critical US systems, according the National Security Agency director.
The possibility of such cyber attacks by US adversaries has been widely known, but never confirmed publicly by the nation's top cyber official.
At a hearing of the House intelligence committee, Admiral Michael Rogers, NSA director and head of US Cyber Command, said adversaries are performing electronic "reconnaissance" on a regular basis so that they can be in a position to disrupt the industrial control systems that run everything from chemical facilities to water treatment plants.
"All of that leads me to believe it is only a matter of when, not if, we are going to see something dramatic," he said.
Outside experts say the US Cyber Command also has the capability to hack into and damage critical infrastructure, which in theory should amount to mutual deterrence.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
But Rogers, who did not address his offensive cyber tools, said the nuclear deterrence model did not necessarily apply to cyber attacks.
Only a handful of countries had nuclear capability during the Cold War, he said, and nuclear attacks could be detected and attributed in time to retaliate.
By contrast, the source of a cyber attack can easily be disguised, and the capability to do significant damage is possessed not only by nation states but by criminal groups and individuals, Rogers noted.
In cyberspace, "you can literally do almost anything you want, and there is not a price to pay for it", the NSA director said.
Rogers said the Obama administration is seeking to establish a set of international principles governing military cyber operations, such as banning attacks on hospitals.
