The Pentagon has admitted it suffered a major cyber attack in which thousands of files were taken by foreign hackers, BBC reported.
Deputy Defence Secretary William Lynn said that in a March attack and other breaches, hackers had taken information on "our most sensitive systems".
The admission came as the Pentagon rolled out a strategy for strengthening US cyber capabilities and addressing threats and attacks in cyberspace.
The plan would treat cyberspace in a similar manner to land, air and sea.
"In the 21st Century, bits and bytes can be as threatening as bullets and bombs," Mr Lynn said, unveiling the plan.
In a speech at National Defense University in Washington, Mr Lynn said about 24,000 files containing Pentagon data were stolen from a defence industry computer network in March, marking one of the largest cyber attacks in US history.