Cyberattack Estimate: 250K an Hour

Army Gen. Keith B. Alexander, the head of the new U.S. Cyber Command, estimates that bad actors now probe Defense Department networks and systems 250,000 times an hour -- or some 6 million times a day. Or this: 2.19 billion times a year.

Alexander, who also runs the National Security Agency in his spare time, said in a speech on Thursday at the Center for Strategic and International Studies in Washington that operations in cyberspace have become a critical element of national and military power and protecting the networks is essential to national security.

Based on statistics Alexander presented, the number of probes Defense experiences a day almost matches the number of military computers, some 7 million machines connected to 15,000 networks, with 21 satellite gateways and 20,000 commercial circuits.

Alexander said that at the moment "our front line defenses are up to this challenge." But he said he has concerns about threats to network security from a growing array of foreign actors, terrorists, criminal groups and individual hackers.

"Our data must be protected. . . . We have an enormous challenge ahead of us as a nation, as a department and as a command," he said.