The hacker seems nice: “Anyways, that's all for now. I hope this series of issues has given you some good ideas for how to prevent this level of compromise in the future. Security doesn't work retroactively, but I believe in you and I think you'll come back from this even stronger than before. Or at least, I hope so -- My own information is in this user table.” https://github.com/matrix-org/matrix.org/issues/365
That gives a 404 now. I'm not enormously happy with GitHub's willingness to completely hide bug reports like this...
Looks like it wasn't cached by Google either.