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A US Air Force version of the F-35 Lightning II takes off from the Fort Worth Joint Reserve Base in Texas.The Pentagon’s top supplier is experiencing a major disruption to its computer systems. The issue could be related to network security. Image Credit: Reuters

Washington/Boston: Lockheed Martin, the Pentagon's No 1 supplier, is experiencing a major disruption to its computer systems that could be related to a problem with network security, a defence official and two sources familiar with the issue said on Thursday.

Lockheed, the biggest provider of information technology to the US government, is grappling with "major internal computer network problems," said one of the sources who was not authorised to publicly discuss the matter.

A second source, who also asked not to be identified, said the issue was "affecting a lot of people" at Lockheed, maker of the stealthy F-22 and F-35 fighter planes and other critical weapons systems.

Lockheed notified the Pentagon about the problem and its response, including resetting passwords for employees, said the defence official, who was not authorised to speak publicly.

Pentagon officials were working closely with Lockheed to gather data about the situation and "any action to be taken," the official added.

Lockheed, which employs 126,000 people worldwide and had $45.8 billion in revenues last year, said it does not discuss specific threats or responses as a matter of principle, but regularly took actions to counter threats and ensure security.

"We have policies and procedures in place to mitigate the cyber threats to our business, and we remain confident in the integrity of our robust, multilayered information systems security," said spokesman Jeffery Adams.

Big corporations — especially government contractors — keep matters of internal security secret and rarely publicly disclose problems in securing their networks.

Yet companies do occasionally reveal such attacks, sometimes forced by financial disclosure laws or by the large impact on customers.

Sony Corp, for example, last month disclosed that hackers had accessed personal data of some 100 million customers and was forced to shut down its PlayStation Network online gaming system.

The sources said Lockheed employees were still able to use mobile devices to access their company email accounts.

The slowdown began on Sunday after security experts for the company detected an intrusion to the network, according to technology blogger Robert Cringely. He said it involved the use of SecurID tokens that employees use to access Lockheed's internal network from outside its firewall,