Defence contractor Lockheed Martin has warned that the danger from cyber-attacks has increased significantly, after it recorded a big rise in the number of threats to its own systems.
The firm, the Pentagon's number one defence supplier, says 20 per cent of threats directed at its networks are "advanced and persistent".
"The number of campaigns has increased dramatically over the last several years," said vice president and chief information security officer Chandra McMahon. "The pace has picked up," she added.
She refused to comment on where the attacks are coming from, although China and Iran are suspected, but admitted the number of attacks had grown and they were often becoming increasingly coordinated.
The news comes after US Defence Secretary Leon Panetta warned the nation's infrastructure is at risk of a "cyber-Pearl Harbour".
Lockheed Martin is at risk through hackers targeting its suppliers, McMahon said, adding that the firm had seen some "very successful attacks" against a number of them. A high-profile cyber-attack against the firm in May 2011 came after systems of two of its suppliers, RSA and an unnamed company, were compromised.
"The adversary was able to get information from RSA and then they were also able to steal information from another supplier of ours, and they were able to put those two pieces of information together and launch an attack on us," said McMahon.
The defence contractor is now helping the companies to improve their security, and is sharing security best practice with other defence firms and suppliers.
"It's just one example of how the adversary has been very significant and tenacious and has really been targeting the defence industrial base," she added.