WhatsApp have of late being advertising its adoption of end to end encryption in its messaging client which it says would keep your messages away from the prying eyes of hackers. However from the demonstration videos below, one can see that promise of security might have been made a bit too soon, as a the video shows that hackers can gain access to other people's WhatsApp acccount. However the blame doesn't solely lie with WhatsApp (although its association of users with their numbers makes it possible), a huge chunk of the blame should go Telecoms Operators whose use of SS7 (Signalling System 7) as a central hub for connection makes it possible to hack a person's WhatsApp account.
In the hack the hacker spoofs the victim's number using an SS7 vulnerability and convinces the WhatsApp client to switch the victim's WhatsApp to his phone.
This enables him not only to respond to messages from people trying to reach the victim but also to see past WhatsApp messages that have been backed up. However it signs out the victim's device which could be a problem for the hacker if the victim tries to reconnect his WhatsApp.Besides WhatsApp, the hackers were also able to execute a similar hack on Telegram.Telegram users would fare a bit worse off than WhatsApp users as they would be oblivious to any hack unlike WhatsApp users who get signed out.

Check out the source link for the videos showing The WhatsApp and Telegram apps being hacked

Source

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