We want to share with you this interesting text wrote by Jochem (a member of
When you join a public group and post there: keep in mind that anyone can read this, even without joining the group. There is a minimal expectation of privacy in public groups, as they are essentially open to the outside world (this even includes scary entities like the NSA, because they also live on our planet).
The openness of Telegram's clients and API allows anyone to write a third-party tool to download and store chat history of any public and private groups they can access. While private groups are usually not accessible to anyone without an invite or invite link, public groups can be crawled easily without anyone noticing.
This does not mean the NSA is spying on Telegram users, and all anyone potentionally could see are: Your profile pictures; Your first and last name; The messages you and others posted in public groups. Private groups and chats are safe as always, as long as invite links are kept private. Secret chats can't be touched by crawlers.