Chinese hackers have gained access to some advanced weapons systems, that include the Patriot missile system, the Navy's Aegis ballistic missile defense systems, the F/A-18 fighter jet, the V-22 Osprey, the Black Hawk helicopter and the F-35 Joint Strike Fighter.

Reuters cites a report prepared for the Defense Department by the Defense Science Board, the Washington Post said the compromised U.S. designs included those for combat aircraft and ships, as well as missile defenses vital for Europe, Asia and the Gulf.

The report did not specify the extent or time of the cyber-thefts or indicate if they involved computer networks of the U.S. government, contractors or subcontractors.

But the espionage would give China knowledge that could be exploited in a conflict, such as the ability to knock out communications and corrupting data, the Post said. It also could speed China's development of its defense technology.

China dismissed the report as groundless.

China also dismissed as without foundation a February report by the U.S. computer security company Mandiant, which said a secretive Chinese military unit was probably behind a series of hacking attacks targeting the United States that had stolen data from 100 companies.