Lockheed Martin has admitted that its network was infiltrated by hackers, but the company insisted that the attempt was thwarted before any critical data was stolen.
US weapons manufacturer said that the attack was "significant and tenacious."
According to the company, its information security team detected the attack almost immediately, and took aggressive actions to protect all systems and data.
"No customer, programme or employee personal data has been compromised," the company claims.
Lockheed Martin said at the weekend its team was continuing "to work around the clock to restore employee access to the network, while maintaining the highest level of security."
Lockheed manufactures some of the most sophisticated US military hardware, including the F-35 Joint Strike Fighter and the F-22 Raptor. It is also a major international supplier of military equipment.
Officials at Lockheed and RSA Security, a division of the EMC Corporation that provides the SecurID brand of electronic access tokens, said they were working with federal officials to investigate how the attack occurred and who was behind it.
Last month, Sony’s PlayStation Network was hacked, forced to shut down for weeks, and user credit card numbers were likely stolen.
