'Cybergeddon' fear stalks US

Cyber attacks pose the greatest threat to the United States after nuclear war and weapons of mass destruction - and they are increasingly hard to prevent, FBI experts said on Tuesday.

Shawn Henry, assistant director of the FBI's cyber division, said that computer attacks pose the biggest risk "from a national security perspective, other than a weapon of mass destruction or a bomb in one of our major cities."

"Other than a nuclear device or some other type of destructive weapon, the threat to our infrastructure, the threat to our intelligence, the threat to our computer network is the most critical threat we face," he added.