Telegram was the subject to a lot of controversies over its encryption protocol.Then in 2015, a security researcher published a research paper detailing theoretical weaknesses* in MTProto and concluded that Telegram shouldn’t have tried to roll their own encryption.This means if you're chatting in secret mode on a specific smartphone, you won't see previous messages on your desktop.
In October 2016, the Signal protocol was reviewed by an international team of security researchers and got glowing reviews.
Reading the above, you might think you are fine since Whats App, Facebook Messenger, and Google Allo also use the Signal Protocol. Facebook Messenger and Google Allo don’t enable end-to-end encryption by default.
The feature can be turned on when starting a new message within Messenger.
You'll need to make sure you install the latest version of the i OS and Android app to get it.
Messages will only be kept secret if both users have the updated versions.