The US Pentagon has admitted 24,000 files were stolen from a defence contractor's systems in March, with officials suggesting the attack came from a foreign Government.
The revelation came from William J Lynn, US deputy defence secretary, who was outlining the new Department of Defence Strategy for Operating in Cyberspace yesterday.
"It is a significant concern that over the past decade, terabytes of data have been extracted by foreign intruders from corporate networks of defence companies," Lynn said.
"When looking across the intrusions of the last few years, some of the stolen data is mundane, like the specifications for small parts of tanks, airplanes, and submarines. But a great deal of it concerns our most sensitive systems, including aircraft avionics, surveillance technologies, satellite communications systems, and network security protocols."
He claimed the US had a "pretty good idea" about who was behind the attack in March, but didn't disclose any names, the Daily Telegraph reported.
Lynn said the country's critical infrastructure had also been "probed," noting how the military relied on much of the same electricity and communications technology as US citizens did.
"Significant disruptions to any one of these sectors could impact defense operations. A cyber attack against more than one could be devastating," he added.
"The integrity of the networks that undergird critical infrastructure must therefore be considered as we assess our ability to carry out national security missions."
As has been previously outlined by the US Government, Lynn indicated cyber attacks may be responded to with physical force.
"It would be irresponsible, and a failure of the Defence Department's mission, to leave the nation vulnerable to a known threat. Just as our military organises to defend against hostile acts from land, air, and sea, we must also be prepared to respond to hostile acts in cyberspace," he added.
"Accordingly, the United States reserves the right, under the laws of armed conflict, to respond to serious cyber attacks with a proportional and justified military response at the time and place of our choosing."
The UK Government has been battered with cyber attacks of late.
Earlier this year, Foreign Secretary William Hague admitted it had been hit by the notorious Zeus Trojan.
Chancellor of the Exchequer George Osborne recently revealed in 2010, there were hundreds of serious and pre-planned attempts to break into the Treasury's computer system by "hostile intelligence agencies."
