NSA head: Defense Department weathered 'year of the hacker'

While 2011 could be considered the "year of the hacker," government efforts prevented cyberattacks from having any major effect on Defense Department systems, Gen. Keith Alexander, head of U.S. Cyber Command, planned to tell a House subcommittee on Tuesday.

Still, cyberthreats remain a serious concern, Alexander said in testimony prepared for the House Armed Services Subcommittee on Emerging Threats and Capabilities.

"We believe it is only a matter of time before someone employs capabilities that could cause significant disruption to civilian or government networks and to our critical infrastructure here in the United States," said Alexander, who oversees the National Security Agency.

With parts of the defense budget on the chopping block, officials have largely been successful in preventing cuts to cybersecurity.