spica.wrk.ru

'When registering an account with #Telegram, the app helpfully uploads the entire Contacts database to Telegram's servers (optional on iOS).

This allows Telegram to build a huge social network map of all the users and how they know each other.

It is extremely difficult to remain anonymous while using Telegram because the social network of everyone you communicate with is known to them (and whomever has pwned their servers).'

more reasons why telegram is not a good choice for secure messaging:
https://gitlab.com/edu4rdshl/blog/blob/master/why-telegram-is-insecure.md
#infosec