Not really. It's just marketing push that 'Telegram is the most secure messenger' that somehow does the job, and the unwitting public is happy to accept it as a fact.
As of source code... do you really need a source code if you can login with just your username/password and instantly see all your chats? For anyone who has some remote understanding of the matter it clearly tells that chat history is stored on servers without meaningful encryption and that server owner can access all chat history at will.
As of source code... do you really need a source code if you can login with just your username/password and instantly see all your chats? For anyone who has some remote understanding of the matter it clearly tells that chat history is stored on servers without meaningful encryption and that server owner can access all chat history at will.