Lockheed Martin, the largest defence contractor in the US, revealed this weekend that it fell victim to a successful cyber attack.

The company, which is also the US government’s top IT supplier, said that no personal data was stolen thanks to swift action taken when the attack was detected on 21 May. "The information security team detected the attack almost immediately, and took aggressive actions to protect all systems and data," Lockheed said in a statement.

Unconfirmed reports have linked the breach to a separate cyber attack on security provider RSA Security in March, in which web security certificates were stolen by hackers.

After that breach, RSA CEO Art Coviello said that the stolen information could not be used to carry out a direct attack. However, he did say that the stolen data "could potentially be used to reduce the effectiveness of a current two-factor authentication implementation as part of a broader attack."

It is still unclear how the attacks were carried out, but officials at Lockheed and RSA say they are working with federal officials to uncover the source and method of the attacks.EMC, the umbrella company for RSA Security, said that it was too early to speculate on the cause of the breach at Lockheed.

The incident is the latest in a string of attacks that could have national security implications. Last month, a nuclear research facility in the US fell victim to an "advanced persistant threat", a style of cyber attack commonly linked (through circumstantial evidence) to Chinese intelligence agencies.