The fun part is they don't know the extent of the comprise or how long it has been going on.
What happened is that CISA recently published a report stating that they think a lot of US telecommunications equipment has been compromised. It isn't a one time breach. They know that China has control over a unspecified amount of critical components. The malware China is using is extremely complex and very hard if not completely impossible to detect. China is very good at covering there tracks so even getting a sample of Malware is hard.
Because of all this, CISA is now recommending that people use encrypted messagers.
Matrix is not always encrypted.
Signal, Simplex chat or any other well vetted messager. Avoid Telegram as it isn't encrypted and is tied to Russia.
Whut? When is matrix not encrypted somtetimes? Genuine question - I'm a matrix newbie and i thought that all was encrypted was the whole point O.o
On the transport level it is encrypted but not on the server. To get E2EE you need to turn it on.
It's been on by default for many years now.