Metadata is all data that’s involved in communication other than the actual content, e.g., any available information about sender and recipient, message properties, plus date and time and other circumstances of the transmission. Facebook, the owner and operator of WhatsApp, is financed by selling targeted ads and therefore has an economical interest in metadata that’s as telling as possible. By systematically collecting metadata and combining it with data from other services (e.g., Instagram), detailed user profiles can be created. Thanks to these user profiles, ads can be sold at high prices because they can be targeted to specific demographics.
Threema is based on a transparent business model that’s compatible with the “Privacy by Design” credo. The service is financed by the sale of the app, i.e., the users pay for the service. The system was designed from the ground up with security and metadata reduction in mind. Only data that’s necessary for the service operation is generated and never stored longer than technically required.