Richard Clarke, a cyber security expert and ABC News consultant, said he was not surprised at the weapon systems that were targeted, but said the danger from Chinese hackers is "very much a major concern" for the U.S. government for three reasons:
First, he said that by just stealing technological secrets, the Chinese military is saving billions of dollars on research and development costs for their own systems. He pointed to the apparent similarities between advanced U.S. systems -- like the stealth F-35 Joint Strike Fighter -- and new Chinese programs -- like their J-20 stealth fighter, as well as strikingly similar drone platforms.
Second, Clarke said the government is concerned the Chinese could use the stolen information to find vulnerabilities in the American military assets.
As Frank Cilluffo, director of George Washington University's Homeland Security Policy Institute, put it, the Chinese want to "discover the Achilles heel of our weapons systems and defenses."
Lastly, Clarke said there is concern the Chinese may have been able to penetrate the supply chain for major weapons systems and installed cyber back doors in the components before going into the final weapon system.
John Pike, Director at GlobalSecurity.org, told ABC News it's unlikely the most sensitive information about the weapons programs was stolen because that information resides on Pentagon servers, not with the private companies that have allegedly been hacked. He also said that in some cases China is so far behind in developing similar technology that "even if they did acquire the most technically sophisticated data, I'm not sure they'd know what to do with it."
But Cilluffo pointed out another, more specific potential impact the breach may have in the Pacific.
There, he said, Secretary of Defense Chuck Hagel has ordered America's Theater High-Altitude Area Defense (THAAD) missile defense system to Guam in response to recent North Korean missile tests. The THAAD system is listed among those compromised by the Chinese hackers, raising the possibility that any compromising information on the advanced system could be shared between the friendly Asian nations.
Lockheed Martin, America's largest defense contractor, said in a statement to ABC News that the company "remains confident in the integrity of our robust, multi-layered information systems security."
A representative for another major defense contractor, Northrop Grumman, declined to comment on the allegations agains the Chinese, but said they've seen the number of attempts to breach our networks "increasing at an alarming rate."
Boeing declined to comment and directed all inquiries to the Defense Department.