Lack of server source code: https://telegram.org/apps#source-code

Lack of security: https://security.stackexchange.com/q...re/49802#49802

Turns out indeed nothing is ever end-to-end-encrypted on Telegram by default, which is made exponentially worse by the fact that they've now effectively given the Russian government backdoor access to everything: https://www.bloomberg.com/news/artic...ncryption-keys

Coins and money: https://www.theverge.com/2018/4/1/17...tocurrency-ton