NEW YORK — Lockheed Martin has admitted it was the recent target of a "significant and tenacious" cyber attack, although the defense contractor and the Department of Homeland Security insist the hack was thwarted before any critical data was stolen. But what about next time? With top-secret military programs at stake, staying a step ahead of ever-evolving cyber spies is a matter of national security. Information security experts say the rash of cyber attacks this year — including a massive security breach at Sony Corp. last month that affected millions of PlayStation users — has emboldened hackers and made them more willing to pursue sensitive information.

NEW YORK — Lockheed Martin has admitted it was the recent target of a "significant and tenacious" cyber attack, although the defense contractor and the Department of Homeland Security insist the hack was thwarted before any critical data was stolen. But what about next time? With top-secret military programs at stake, staying a step ahead of ever-evolving cyber spies is a matter of national security. Information security experts say the rash of cyber attacks this year — including a massive security breach at Sony Corp. last month that affected millions of PlayStation users — has emboldened hackers and made them more willing to pursue sensitive information.

"This year has really lit up the boards in terms of data breaches," said Josh Shaul, chief technology officer at Application Security, a New York-based company that is one of the largest database security software makers. "The list of targets just grows and grows."

Lockheed Martin Corp. said in a statement Saturday that it detected the May 21 attack "almost immediately" and took countermeasures.

"Our systems remain secure; no customer, program or employee personal data has been compromised," the Bethesda, Md.-based company said. Neither Lockheed Martin nor federal agencies would reveal specifics of the attack, or its origins. Company spokeswoman Jennifer Whitlow declined to comment further on the case Sunday.

This isn't the first time Lockheed Martin has been targeted. Nearly four years ago, officials revealed that hackers had breached Lockheed's high-tech Joint Strike Fighter program. Officials said that no classified information about the military program was compromised, but heightened protections were added. Analysts said the latest attack likely would spur rival defensive contractors like Northrop Grumman Corp., Raytheon Co., General Dynamics Corp. and Boeing Co. to take additional steps to safeguard their systems.

"I guarantee you every major defense contractor is on double alert this weekend, watching what's going on and making sure they're not the next to fall victim," Shaul said.

Boeing declined to comment on the company's network security measures. Northrop Grumman spokesman Randy Belote said in an e-mailed statement that "we do not comment on whether or not Northrop Grumman is or has been a target for cyber intrusions," adding that the company "continuously monitors and proactively strengthens the security of our networks."

Over the past several years, the U.S. government has become more aggressive in its efforts to tackle cybercrime, developing strategies to beef up government computer systems, expand cooperation with other countries and improve coordination with the private sector. Cybersecurity was declared a top priority by President Barack Obama shortly after he took office in 2009, setting off several government-wide reviews to develop strategies to frame how the U.S. will better secure government, business and public online activity.

The Pentagon last May set up a new Cyber Command, based alongside the National Security Agency at Fort Meade, Md., in recognition of the expanding threat against the Defense Department and the need to better coordinate the nation's offensive and defensive cyber operations. The Department of Homeland Security also is slowly employing an automated system — known as Einstein 2 and Einstein 3 — to protect government agencies' computer systems.

Still, the attacks have continued. William J. Lynn III, the deputy defense secretary, said in January that more than 100 foreign intelligence agencies have tried to breach U.S. defense computer networks, largely to steal military plans and weapons systems designs.

Attacks against corporations have been growing this year. In March, RSA, the security division of data storage company EMC, acknowledged that its computer network was hacked. The implications are serious because RSA's technology underpins the security of some of the world's most closely guarded data. RSA makes small security devices that supply constantly changing numbers that are used as secondary passwords for accessing corporate networks and email.

Last month, more than 100 million online accounts were affected by a hacking of Sony's PlayStation Network gaming service and other online services.

Companies have gotten better at detecting attacks through so-called "intrusion software" that uncovers odd behavior on networks, said Alfred Huger, vice president of development at security firm Sourcefire. As recently as five years ago, Huger said it was difficult for companies to determine if they were being hacked.

Still, even with the enhanced technology, experts say cyber espionage will continue and evolve. Rich Mogull, analyst and CEO of Phoenix-based security research firm Securosis, noted that governments and defense agencies have been spying on each other throughout history. Computers have just made it easier to do so electronically.

"This is just what countries do," he said. "It's the unfortunate reality of how the world works."

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Baldor reported from Washington.

AP-WF-05-29-11 2215GMT