I stumbled upon this question [0], which is currently unanswered. Since WhatsApp is bought by Facebook many people look for an alternative (although I don't know why now; their data hasn't been secure before that deal either). There have been great, insightful comments about Telegram's security[1] and I hope some of the experts here can formulate some sentences to enlighten the common internet user.
(Peoply tend to trust apps based on too many subjective factors.)[0] http://security.stackexchange.com/questions/51953/is-threema-secure
[1] https://news.ycombinator.com/item?id=6916860