The US Department of Defense (DoD) has claimed that all classified data about the F-35 Lightning II joint strike fighter (JSF) programme remains secure despite the alleged hacking attempts by China.

Last week, the US National Security Agency intelligence whistleblower Edward Snowden leaked documents claiming the Chinese hackers stole as much as 50TB of classified data about the fifth-generation aircraft, including radar designs and engine schematics.

However, the F-35 Program Office said the documents published by Der Spiegel ‘rehashed’ a previously disclosed and reported 2010 incident that compromised only non-classified data about the F-35.

In a statement to Reuters, the office said the fighter’s ability to survive cyber attacks was ‘foundational to the programme’s development, remains robustly resourced, and will continue to be a priority for the department.’

F-35 manufacturer Lockheed Martin refused to comment on the Spiegel report, but noted that it carefully monitored and protected its computer networks against an array of cyber attacks and regularly shared the data with the US Government, public utilities and other companies.

"The data was apparently used by China to manufacture its own advanced fighter jets."

According to the media reports, the hackers specifically stole the data about the fighters designed for the Australian Defence Force (ADF) and the Australian Government was aware of the ‘serious damage’ caused due to the breach.

The data was apparently used by China to manufacture its own advanced fighter jets, with some defence experts claiming that China’s domestic stealth jets had design elements resembling the F-35.

However, China has denied allegations that it had stolen sensitive data for the Pentagon’s $399bn programme.

Chinese Foreign Ministry spokesman Hong Lei said: "The so-called evidence that has been used to launch groundless accusations against China is completely unjustified.

"According to the materials presented by the relevant person, some countries themselves have disgraceful records on cyber security."

Apart from F-35, the cyber espionage also targeted a range of US advanced weapons programme, including the Aegis Ballistic Missile Defense System, Littoral Combat Ship designs and emerging railgun technology, as reported by RT.

Image: Chinese hackers allegedly stole as much as 50TB of classified data about F-35 fighter, including radar designs and engine schematics. Photo: courtesy of Andy Wolfe.