[Ask HN] Is Threema Secure?

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