June 20, 2013 -- A top Pentagon official said the cyber theft of unclassified design information about the F-35 Joint Strike Fighter is a "major problem," but added he was confident that classified information about the military's next-generation stealth warplane was "well protected."

The official said the information gleaned about the aircraft could speed up the time it takes for a potential adversary to develop a similar aircraft of its own.

A Pentagon report recently cited the aircraft among many weapons systems whose unclassified designs may have been the targets of cyber espionage. The information was stored on the computer systems of the defense contractors involved in designing the weapons systems.

At a Senate appropriations subcommittee hearing Wednesday, Frank Kendall, the Defense Undersecretary for Acquisition, Technology and Logistics, said the theft of unclassified information was a "major problem for us," but he was confident that classified information about the plane was "well protected."

The Pentagon is planning to buy as many as 2,450 of the aircraft that will be the warplane of the Air Force, Navy and Marines. Cost overruns and production delays have pushed the price tag of each aircraft to almost $137 million.

When asked by Sen. Jack Reed, D-R.I., if the aircraft's technology had been compromised by the cyber-theft, Kendall said he was "reasonably confident" that the plane's classified information was "well protected."

But he also said, "I'm not at all confident that our unclassified is as well protected." He explained some of the plane's information was unclassified "because it's not as sensitive or important." However he said he was concerned "with the loss of design information that's at the unclassified level."

He said he was going to institute stronger consequences "for our contractors who don't protect that information well enough. Part of that is being stolen right now, and it's a major problem for us."

Kendall said that access to that information could lead to a reduction in "cost and lead time of our adversaries to doing their own designs. So it gives away a substantial advantage."

It's not "as much as specific vulnerability that we would see," he said. "It's that the amount of time and effort they're going to have to put into getting their next design, and staying with us -- and as you're probably well aware, at least two nations are well into developing fifth-generation aircraft right now. So that's a concern."

Those two nations? Kendal didn't say but China and Russia have been developing that kind of stealth aircraft.