Apart from manufacturing fighter planes and spy satellites, some of the company's various subsidiaries provide secure computer access to numerous federal and military departments and agencies.
From its headquarters in Bethesda, Md., the company said security staff "detected a significant and tenacious attack on its information systems network" Saturday.
"As a result of the swift and deliberate actions taken to protect the network and increase IT security, our systems remain secure; no customer, program or employee personal data has been compromised," the company said.
In March, there was a hacker attack on RSA Security, which provides SecurID security tokens to millions of customers who access computers outside their offices. Sources told The New York Times that attack could be linked to previous attempts to infiltrate Lockheed Martin's systems.
Other major military contractors such as General Dynamics Northrop Grumman and Boeing wouldn't discuss their security response to the growing number of attacks, the Times said.