BETHESA, MARYLAND (BNO NEWS) -- Hackers targeted Lockheed Martin Corp., a major U.S. defense contractor which holds highly sensitive information, in a 'significant and tenacious' attack earlier this month, the company said on Sunday.

Both the U.S. government and Lockheed Martin confirmed the attack on early Sunday morning after several media reports emerged about the attack. Few details were released, but the company said its data remained secure.

Lockheed Martin said the 'significant and tenacious' attack on its information systems network was detected on May 21. "The company's information security team detected the attack almost immediately, and took aggressive actions to protect all systems and data," Lockheed Martin said in a statement.

The company said that, as a result of 'swift and deliberate' actions taken to protect the network and increase IT security, its systems remained secure. "No customer, program or employee personal data has been compromised," a statement said.

"Throughout the ongoing investigation, Lockheed Martin has continued to keep the appropriate U.S. government agencies informed of our actions. The team continues to work around the clock to restore employee access to the network, while maintaining the highest level of security," the statement added.

Chris Ortman, a spokesman for the U.S. Department of Homeland Security, said it was aware of the cyber attack. "Together with the Department of Defense, [DHS] has been in contact with the company to offer assistance in determining the extent of the incident, performing analysis of available data in order to provide recommendations to mitigate further risk," he said.

A DHS source said the agency's cyber response teams can perform a preliminary diagnosis of the compromise. "At the company's request, DHS can deploy a team to meet with the affected organization to perform analysis of the infected systems, develop mitigation strategies, advise asset owners and operators on their efforts to restore service, and provide recommendations for improving overall network security," the official said.

Lockheed Martin is a global security company that employs about 126,000 people worldwide and is principally engaged in the research, design, development, manufacture, integration and sustainment of advanced technology systems, products and services. It is the Pentagon's No. 1 supplier by sales.

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