Top defense official details previously classified cyberattack . The U.S. government has been warning for months that North Korea is developing a new generation of nuclear weapons and could strike the United States or its allies with them. U.S. Cyber Command , other steps are part of the response .
Top defense official details previously classified cyberattack . Infected flash drive in laptop infiltrated Defense Department systems . U.S. Cyber Command , other steps are part of the response .