The US aerospace group Lockheed Martin has revealed that it had to fight off a "significant and tenacious" cyber attack on its systems last week.
The group detected the attack on its information systems network just over a week ago and took "aggressive actions to protect all systems and data".
Lockheed, which makes the Trident missile and F-22 Raprtor fighter jet, is the Pentagon's top supplier by sales, and said it had kept the appropriate government agencies informed.
A spokesman for the US Defence Department said the impact of the attack had been "minimal and we don't expect any adverse effect".
A spokeswoman for the group said: "As a result of the swift and deliberate actions taken to protect the network and increase IT security, our systems remain secure." She went on to add: "No customer, program or employee personal data has been compromised."