Based on the timing of the attacks and clues in the computer code, researchers with the firm Symantec believe the Chinese did not steal the code but captured it from an N.S.A. attack on their own computers — like a gunslinger who grabs an enemy’s rifle and starts blasting away.
https://www.nytimes.com/2019/05/06/us/politics/china-hacking-cyber.html
https://original.antiwar.com/Chas_Freeman/2019/05/06/on-hostile-coexistence-with-china/