These sorts of documents are generally long and complicated. The General Terms and Conditions ( GTCs) or the Privacy Policy lay out what the provider does with its customers' data. This allows profiles to be created that can be used for the purposes of personalised advertising.

This sort of data is not just used to correctly direct the message but can also be used to analyse preferences and for similar purposes. The metadata includes the identifier of the sender, often in the form of their telephone number, the identifier of the intended recipient, the date and the time. The messages that can be sent via messengers consist of the text of the message, any file attachments, such as photos, and what is referred to as metadata. However, with these types of free messengers, users must check for themselves whether their provider actually supports the desired encryption technology. In addition, no telephone number is required for these chat systems. The main difference between these and the closed systems mentioned above is that you can choose your preferred provider from the large number of options but still chat across different messengers with anyone that uses the same protocol. There are also open systems that are not specific to a particular provider and that are based, for example, on the XMPP or Matrix communication protocols. Closed messengers mostly use similar encryption methods, with not all providers using full end-to-end encryption for all of their functions.

Closed systems like these allow people who use the same messenger system to chat. Well-known instant messengers include WhatsApp, Threema, Telegram, iMessage, Signal and Facebook Messenger.

What to bear in mind when using messengers.

Encrypted messengers