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.
Note even with all of this they only recommend they use encrypted messaging. We should merrily go along with fb messenger or sms or whatever they swear is good.
They recommended Signal:
https://www.forbes.com/sites/zakdoffman/2024/12/03/fbi-warns-iphone-and-android-users-stop-sending-texts/
btw messenger isn’t the worst case scenario. 1-1 chats are e2ee.
it’s still facebook and it sucks, but it’s not as bad as SMS/calls