Panetta Warns of Dire Threat of Cyberattack on U.S. - NYTimes.com

Also see The Dangers of Allowing an Adversary Access to a Network

"In August, a cybersecurity bill that had been one of the administration’s national security priorities was blocked by a group of Republicans, led by Senator John McCain of Arizona, who took the side of the U.S. Chamber of Commerce and said it would be too burdensome for corporations.
The most destructive possibilities, Mr. Panetta said, involve “cyber-actors launching several attacks on our critical infrastructure at one time, in combination with a physical attack.” He described the collective result as a “cyber-Pearl Harbor that would cause physical destruction and the loss of life, an attack that would paralyze and shock the nation and create a profound new sense of vulnerability.”"

Panetta Warns of Dire Threat of Cyberattack on U.S. - NYTimes.com