Called Telegram, the German app offers "secret chats" that use end-to-end encryption. The company aids key exchange but does not hold the encryption keys itself and cannot decrypt any of the messages, the Verge reported.

Authorities in South Korea recently announced a crackdown on messages seen as insulting to the president or even "rumour-mongering". Prosecutors have started actively monitoring chats for violations, promising punishment for anyone spreading inappropriate content.

Nearly 15 lakh new South Korean users have signed up to use the app in the past week, the report added.

The app has more than 5 crore users worldwide."People frequently come to Telegram looking for extra security -- some of them from countries with censorship issues," Markus Ra from Telegram was quoted as saying.