Dr. David von Oheimb is a German IT security expert and privacy advocate.
In short words, he advises strongly against using WhatsApp and Viber and to better use Threema, TeleGuard, Signal, Telegram (but only with “secret chats” activated), and/or Conversations. These provide not only excellent cryptography but also much better privacy, in particular Threema and TeleGuard.
This is what he writes:
Threema has been designed for security, privacy, and informational self-determination. It can be used really anonymously. It is paid but inexpensive. Like with WhatsApp, its web client is rather inconvenient to use because your smartphone must be active as well.
Signal is technically similarly secure as Threema. Unfortunately it is US-based, so American authorities have access to the service provider’s data.
Conversations is highly secure and supports open standards.
Telegram is independent of Western commerce and politics. Security experts have warned agaist using it. Telegram provides end-to-end security only for “secret chats” with individual contacts, and for each recipient such a chat needs to be explcitly started first. Such chats can be used only on the smartphone, whereas normal ones also work with the desktop client.
Wire is oriented at business communication but also offers a free and very secure IM, allowing conventient (even parallel) use on multiple devices. Ownership was transferred from Europe to the USA in 2019, which has undermined trust in its privacy protection.
Viber offers end-to-end encryption like WhatsApp but exhibits the same evil behavior in terms of privacy.
A comparison list of all instant message apps can be found on Wikipedia.
Check out Dr von Oheimb´s website for more information, here https://perlen.davoh.de/IM/index.html
Martin “Messenger” Schweiger