US defense contractor Lockheed Martin has confirmed that it had detected "a significant and tenacious" attack on its information systems network.
"Lockheed Martin detected a significant and tenacious attack on its information systems network," said a company statement.
The company's information security team detected the attack almost immediately and took what is described as "aggressive actions" to protect all systems and data, the statement added.
"As a result of the swift and deliberate actions taken to protect the network and increase IT security, our systems remain secure," Lockheed Martin said.
"No customer, program or employee personal data has been compromised."
The incident was under investigation, and Lockheed Martin said it was keeping appropriate US government agencies informed of situation. It did not mention any suspected source of the cyber-attack.
The company said that despite the attack, it remained confident in the integrity of its "robust, multi-layered information systems security."
Headquartered in Bethesda, a Maryland suburb of Washington, Lockheed Martin employs about 126,000 people around the world. It focuses on design, development, and manufacturing of advanced technology systems, including some of the most advanced weaponry.
It is one of the world's largest defense contractors, with about 74 percent of its revenues in 2009 coming from military sales, according to published reports.
Lockheed Martin's products included the Trident missile, P-3 Orion spy plane, F-16 and F-22 Raptor fighter jets and C-130 Hercules military cargo plane among many other major weapons systems.
The corporation's 2010 sales from continuing operations reached $45.8 billion.
The US space agency NASA announced last week that a new spacecraft to ferry humans into deep space will be based on designs for the Orion crew exploration vehicle and built by Lockheed Martin.
The Orion capsule, originally designed to take astronauts back to the moon, is a surviving component of the Constellation manned space exploration program canceled by President Barack Obama last year for being behind schedule and over budget.
The capsule will weigh 23 tons and NASA has no date set for a potential launch, said Douglas Cooke, associate administrator for NASA's exploration systems mission directorate.
There is also no final cost associated with the project.
Lockheed Martin is to continue its work on building the space capsule begun in 2006.