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Slideshow: 10 Massive Security Breaches

On Saturday, Lockheed Martin released a statement confirming the attack, which it described as "significant and tenacious." But it said its information security team "detected the attack almost immediately and took aggressive actions to protect all systems and data."

As a result, the company said, "our systems remain secure; no customer, program, or employee personal data has been compromised."

Hackers reportedly exploited Lockheed's VPN access system, which allows employees to log in remotely by using their RSA SecurID hardware tokens. Attackers apparently possessed the seeds--factory-encoded random keys--used by at least some of Lockheed's SecurID hardware fobs, as well as serial numbers and the underlying algorithm used to secure the devices.

That suggests that whoever attacked Lockheed Martin may also have been behind the successful breach in March of EMC's RSA division, which manufactures SecurID. "Since then, there have been malware and phishing campaigns in the wild seeking specific data linking RSA tokens to the end user, leading us to believe that this attack was carried out by the original RSA attackers," Rick Moy, president and CEO of NSS Labs, said in a blog post.

According to security blogger Robert Cringely, aka Mark Stephens, who broke news of the attack against Lockheed Martin, "It seems likely that whoever hacked the RSA network got the algorithm for the current tokens and then managed to get a keylogger installed on one or more computers used to access the intranet" at Lockheed Martin. From there, attackers reportedly gained access to the company's internal network.

What types of information might attackers have been targeting? Lockheed Martin, which earned revenue of $45.8 billion in 2010, makes everything from Trident missiles and F-22 fighter jets to a network of satellites for the Department of Defense that are designed to support high-priority wartime communications.

By all accounts, Lockheed Martin's swift detection of the attack helped avert potential disaster. "The good news here is that the contractor was able to detect an intrusion then did the right things to deal with it," Cringely said. "A breach like this is very subtle and not easy to spot." Furthermore, he said, the same day that Lockheed Martin detected the attack, all remote access for employees was disabled, and the company told all telecommuters to work from company offices for at least a week. Then on Wednesday, the company informed all remote workers that they'd receive new RSA SecurID tokens and told all 133,000 employees to reset their network passwords.

In a statement released Sunday, EMC said it was "premature to speculate" on the details of the attack. But if attackers did use information stolen from RSA to hack into the SecurID system used by Lockheed Martin, then EMC could be forced to finally reveal, publicly, any risks that the use of its system might now pose to the 40 million users of SecurID hardware token customers and 250 million users of its SecurID software.

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