More detail on exactly which F-35 systems PLA Unit 61398 has compromised, somewhat ironically coming from stolen NSA reports:
China stole plans for a new fighter plane, spy documents have revealed
The leaked document shows that stolen design information included details of the JSF's radar systems which are used to identify and track targets; detailed engine schematics; methods for cooling exhaust gases; and "aft deck heating contour maps".
In June 2013 US Defense Department acquisitions chief Frank Kendall told a US Senate hearing that he was "reasonably confident" classified information related to the development of the F-35 was now well protected. It is understood the main data breach took place at the prime contractor Lockheed Martin in 2007.
A 2012
Aviation Week report on the hacking claimed that
before the intrusions were discovered nearly three years ago, Chinese hackers actually sat in on what were supposed to have been secure, online program-progress conferences, the officials say.
The full extent of the connection is still being assessed, but there is consensus that escalating costs, reduced annual purchases and production stretch-outs are a reflection to some degree of the need for redesign of critical equipment. Examples include specialized communications and antenna arrays for stealth aircraft, as well as significant rewriting of software to protect systems vulnerable to hacking.