It's well documented. Snowden himself has admitted as much, and it requires no conspiracy — only the stupidity of a single high school dropout.
https://amp.scmp.com/news/hong-kong/politics/article/3178655...
https://amp.scmp.com/news/hong-kong/article/1260306/edward-s...
https://amp.scmp.com/news/china/article/1266821/us-hacks-chi...