Chinese hackers compromised designs for many of America's most sensitive advanced weapons systems, according to a report.
The report prepared for the Pentagon and to officials from government and the defence industry revealed that weapons systems whose designs were breached were programmes critical to US missile defences and combat aircraft and ships.
According to the Washington Post, the report prepared by the Defense Science Board for the Defense Department said that some of the weapons were the backbone of the Pentagon's regional missile defence for Asia, Europe and the Persian Gulf.
Listed weapons in the report whose designs were compromised were the F/A-18 fighter jet, the V-22 Osprey, the Black Hawk helicopter and the Navy's new Littoral Combat Ship, which is designed to patrol waters close to shore.
China, which is pursuing a long-term, comprehensive strategy to modernize its military, is investing in ways to overcome the US military advantage, and cyber espionage is seen as a key tool in that effort.
China has insisted that it does not conduct cyber-espionage on U.S. agencies or companies, and government spokesmen often complain that Beijing is a victim of U.S. cyberattacks, the report said.
President Barack Obama is expected to raise the issue during his meet with Chinese President Xi Jinping next month in California.