Computer spies have reportedly hacked into a Pentagon programme for a new jet fighter.
The Wall Street Journal says cyber-intruders were able to copy vast amounts of data on a $US300 billion Joint Strike Fighter project.
Lockheed Martin is the lead defence firm building the aircraft. Northrop Grumman and BAE Systems are also part of the project.
The aircraft is being developed with financing from the United States, Britain, Italy, the Netherlands, Turkey, Canada, Australia, Denmark and Norway. Other projected early buyers include Israel and Singapore.
The Defence Department says sensitive technology has not been compromised.
The newspaper cites former US officials as saying the attack appears to have originated in China.