They used caller id spoofing and a telco vulnerability.
1. Change your phone ID and try to login on Telegram;
2. Telegram will send an SMS with an authentication number followed by a phone call to the actual mobile phone;
3. To avoid the message going through, spams the victim with many VoIP calls;
4. The Telegram call will be recorded on the missed call voice messages;
In Brazil, you can listen to the recorded messages calling your own number. Surprisingly, the telco only checks if the calling number was equal to the called number.
5. Again, with the call id spoofing, call your own number.
6. Now you have access to the victim's Telegram (past conversations and contact list)
7. ???
8. Profit.
EDIT: I translated part of the transcription used to accuse GG in another thread.
Lauren Sanchez(bezos' new girfiend) along with her brother Michael(who is also her agent), leaked the story to force Bezos to divorce his wife and get along with her.
Explanation 2:
The crown prince of Saudi Arabia personally sent a trojan file, downloaded all the data, distributed it through a gossip rag he happens to be friends with, for some kind of revenge/message
I get why Bezos has to go with explanation 2 because explanation 1 would indicate the girl he wants to have sex with or her brother is manipulative. I dont see why the rest of us have to go along with this. Even this anonymous source says he has "high confidence" not anywhere near certainty.
Would it just be cheaper for these companies to pull out? And what international recourse would happen?
A better site for someone wanting high level discussion on a narrowly focused topic is Reddit, although you will have to choose your subreddits carefully. It can be a difficult needle to thread, but there are quite a large number of quality subreddits once you know how to search.