The latest round of managed information release by Edward Snowden via Spiegel (one of a series) includes the snippet that Chinese security services copied "terabytes" of data about the aircraft. The release states that the compromised information includes radar systems data, engine schematics, heat contour maps, and designs to cool exhaust gases.The latest leak confirms the scale of the data theft, which emerged in US media such as The Washington Times March 2014.
As that report notes, the Defense Science Board at the Pentagon stated that "cyber attacks" had compromised F-35 design information. In 2014, the leak was attributed to Lockheed Martin and was believed to have taken place in 2007
As if we need any more reason to dump this and go make something better