Chinese spies have stolen key designs for the F-35 stealth fighter, according to documents disclosed by former U.S. intelligence contractor Edward Snowden, the Sydney Morning Herald reported Monday.

The report, citing disclosures published by German magazine Der Spiegel, said Chinese cyberspies stole huge volumes of sensitive military information, including “many terabytes of data” about the fighter, such as details of the radar systems it uses to identify and track targets.

The allegation was contained in a top secret U.S. National Security Agency presentation apparently obtained by Snowden.

The F-35 Lightning II is a next-generation fighter set to join the defense fleets of Australia, Japan and other U.S. allies.

It is understood the main data breach took place at prime contractor Lockheed Martin in 2007, predating the orders by both Australia and Japan.

Both countries have selected the F-35 as the next mainstay fighter for their air forces. Japan has 42 on order, while Australia plans to acquire 72.

While this is not the first time this jet has been alleged as a victim of Chinese cyber-espionage, the Snowden documents provide the first apparent confirmation of how much data was compromised, the Sydney Morning Herald said.

It said the leaked NSA briefings confirm that Australia knows of “serious damage” the espionage caused during the F-35’s development.

But it noted that in June 2013, U.S. Defense Department acquisitions chief Frank Kendall told a U.S. Senate hearing that he was “reasonably confident” that such classified information was now well protected.

The stolen information allegedly included detailed engine schematics, methods for cooling the exhaust, and “aft deck heating contour maps.”

Military aviation experts have speculated that the design of China’s new “fifth-generation” fighters — the Chengdu J-20 and the Shenyang J-31 — were extensively influenced by designs stolen from the United States, the report said.

Japan’s government decided in 2011 to procure the F-35. In line with its plan to boost island defense, the Abe administration has allocated ¥103.2 billion to buy six of them in the fiscal 2015 budget.