The instant messaging app does no better than WhatsApp and allows anyone to identify you using your phone number.
” Whose number is this ? ” Everyone has asked themselves the question one day when they receive a call or an SMS from an unknown mobile number. Before going to investigate by searching for said number in Google to hope to find it associated with a professional or an online CV, it is possible to try to identify the person who tried to contact you by following a few trivial steps.
Start by creating a contact card for this number whose owner you do not know, and then let yourself be guided by your favorite messaging applications. It was already known that WhatsApp allows any stranger to spy on you without your knowledge, but that it was possible to prevent this practice by locking their profile information.
Many people then thought that this was not surprising, making a correlation between WhatsApp and Facebook, the social network that has experienced some small concerns about the management and use of its users’ personal data, being owner of WhatsApp.
All applications using a number as an identifier are affected.
The “secure” alternatives like Telegram, however, do not do better. Despite end-to-end conversation encryption (as WhatsApp also does), the app requires you to register with your phone number and does not require you to configure privacy settings on first use. As a result, the technique of creating a contact card on your smartphone to try to identify the number via WhatsApp also works with Telegram.
We experienced this after trying to identify the owner of a number that was not returning any information to WhatsApp. The user had visibly locked his profile, but unfortunately forgot to apply the same precautions with other instant messaging applications using his phone number as an identifier.
We just had to open Telegram to see his profile picture associated with his number. A reverse image search later, we were able to find him on social networks, put a name on his number and face, but also know his professional activity.
Change the default privacy settings before using a new instant messenger
However, locking down your Telegram profile information is simple. Just go to Settings, then Privacy & Security and restrict all privacy-related options to your contacts only. By default, the profile picture is visible to all users. Change the Everyone setting to My contacts so that only contacts in your address book can see your profile picture.
To limit this practice, it would be enough for WhatsApp, Telegram and others to force their users to check their privacy settings, a sine qua non condition to be able to start using the application.