China aims to top U.S. in cyberspace: U.S. general

He attributed the espionage to a mix of criminals, hackers and "nation-state" forces. Virtually all potential U.S. foes also were scanning U.S. networks for trade and defense secrets, he added.

"Everyone but North Korea," he said. "We've concluded that there must be only one laptop in all of North Korea -- and that guy's not allowed to scan" overseas networks, Elder said.

In October, the U.S. Joint Chiefs of Staff defined cyberspace as "characterized by the use of electronics and the electromagnetic spectrum to store, modify, and exchange data via networked systems and associated physical infrastructures."

The definition is broad enough to cover far more than merely defending or attacking computer networks. Other concerns include remotely detonated roadside bombs in Iraq, interference with Global Positioning Satellites and satellite communications, Internet financial transactions by adversaries, and radar and navigational jamming.