Lockheed Martin was hit by a cyber-attack targetting its information systems network last week.
The company's security team detected the threat immediately and took appropriate countermeasures to secure all its systems and data.
"Our systems remain secure. No customer, programme or employee personal data has been compromised," the company said.
The Pentagon and other related US Government agencies are working to establish the extent of the breach.
Lockheed faced a similar attack four years ago when hackers breached its high-tech joint fighter programme, leading to tightened security.
Lockheed Martin is one of the world's biggest aerospace companies and the manufacturer of F-16, F-22 and F-35 fighter jets and warships.