According to the Washington Post, whose reporters obtained a copy of the section, the report doesn't say whether the documents were taken from government or defense contractors' computer networks and systems, or who was behind the attack. It also doesn't say when the attacks happened and how extensive they were.
Still, various senior military and industry officials have apparently confirmed (off the record, of course), that most of these and other attacks against U.S. government targets were initiated by Chinese hackers.
Among the designs stolen were those related to the PAC-3 Patriot missile system, the Terminal High Altitude Area Defense (THAAD) system and the the Navy’s Aegis ballistic-missile defense system, as well as those for the Black Hawk helicopter, the F/A-18 fighter jet, the V-22 Osprey, the Navy’s Littoral Combat Ship, and the the F-35 Joint Strike Fighter.
All this is to be added to the previously disclosed compromises of documents and designs concerning U.S. drone video systems, electronic warfare systems, and more.
The compilers of the report haven't explicitly accused the Chinese government of being behind the attack, but according to the WP, some senior Chinese government representatives were presented with evidence of these and other intrusions a year ago.
Independent defense experts who have taken a look at the entire list have been taken aback by the magnitude of the theft, and say that many of these systems are crucial to protecting the U.S. and its interests and military forces in Asia, Europe and the Persian Gulf.
They also pointed out that this knowledge gives China and its army an operational edge in case of conflict, as well as allows them to spend way less on technology development costs.