you shouldnt trust closed source software also there are numerous complaints about their security model. See http://www.cryptofails.com/post/70546720222/telegrams-crypta... for example. Why not use an open source, cross device alternative? https://www.surespot.me/

Telegram clients (ios,andriod,windows,osx,linux) are open source. Server is closed but client code and protocol provides user with verified secrecy.

Most criticism seems emotion based but no smoking guns. See comments on http://unhandledexpression.com/2013/12/17/telegram-stand-bac... also see response to the post you linked to http://telegramteam.tumblr.com/post/70588130319/telegrams-cr...

anyway i dont work for them and Surespot also looks nice. though nodejs+coffeescript at the server worries me a bit.

I think I mixed up Telegram and Threema so my bad and thanks for the correction/reply.