The competition for the most secure instant messaging tool has been running for years. It re-surfaced this month when WhatsApp announced it has completed implementing end-to-end encryption. Curiously, in security research circles, this has resulted in endless debates between WhatsApp and Telegram. Very much like Emacs vs Vi, everybody has a (strong) opinion, but there is no general consensus. ;)
I think we can agree that Signal, WhatsApp, and Telegram stand out as the most secure messaging solutions - thanks to end-to-end encryption or Perfect Forward Secrecy, for example. This site summarizes the situation quite well.
Yet there is still no good instant messaging tool for enterprises. The main issue is that if you want to share business strategies, source code, or lines of disassembly with your colleagues, it's not convenient to do so over smartphone (or tablet). And unfortunately:
Additionally, I'm not keen on tying an instant messaging account with a mobile phone number for a number of reasons. First, for privacy reasons: who does the phone number get shared with? Contacts? Third parties? Is the location of the phone tracked? etc. And second, for separation reasons: people don't always have a dedicated cell phone line at work. So, this means they end up using their own mobile phone, and consequently their own IM account at work.
Here is a list of pros and cons I have pulled together for this issue.
Source Code: https://telegram.org/apps#source-code
Source Code: https://github.com/WhisperSystem
-- the Crypto Girl