According to the Washington Examiner, a NATO official has stated the obvious when it comes to Telegram’s security:
“Telegram is not really as it used to be,” Janis Sarts, the director of NATO’s Strategic Communications Center of Excellence in Riga, Latvia, told the Washington Examiner. “I do have reasons to believe that there is not full integrity. … Certainly, I would not see it as a secure platform.”
I covered this topic a few months ago when I did a deep dive into the popular messaging and social media platform. I suspect that it’s insecure by design – governments won’t need to ask for user data when they can very easily pluck it off the wire.