Telegram just crossed 100 million users on tuesday. Telegram has been handling 15 billion messages daily and has been seen an additional 350 thousand users added everyday.
In 2003, the app launched iOS and Linux versions and saw a surge in new users. The app also has Snapchat-like self destruct features. Telegram boasts additional crypto security like no other app though some critics say it is prone to metadata leakage.
However, it is more probable that Telegram has gained popularity through its sleek design and usability and not really through its security.