Keep Calm and Send Telegrams!
https://telegram.org/blog/15million-reuters

Certain people checked whether some Iranian numbers were registered on Telegram and were able to confirm this for 15 million accounts. As a result, only publicly available data was collected and the accounts themselves were not accessed.

However, since Telegram is based on phone contacts, any party can potentially check whether a phone number is registered in the system. This is also true for any other contact-based messaging app (WhatsApp, Messenger, etc.).

SMS codes

As for the reports that several accounts were accessed earlier this year by intercepting SMS-verification codes, this is hardly a new threat as we’ve been increasingly warning our users in certain countries about it. Last year we introduced 2-Step Verification specifically to defend users in such situations.

If you have reasons to think that your mobile carrier is intercepting your SMS codes, use 2-Step Verification to protect your account with a password. If you do that, there’s nothing an attacker can do.

NIST blog clarifies SMS deprecation in wake of media tailspin
http://www.epanorama.net/newepa/2016/07/31/nist-blog-clarifies-sms-deprecation-in-wake-of-media-tailspin-zdnet/