Mobile messengers expose billions of users to privacy attacks – Help Net Security

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Popular mobile messengers expose personal data via discovery services that allow users to find contacts based on phone numbers from their address book, according to researchers.

When installing a mobile messenger like WhatsApp, new users can instantly start texting existing contacts based on the phone numbers stored on their device. For this to happen, users must grant the app permission to access and regularly upload their address book to company servers in a process called mobile contact discovery.
A recent study by a team of researchers from the Secure Software Systems Group at the University of Würzburg and the Cryptography and Privacy Engineering Group at TU Darmstadt shows that currently deployed contact discovery services severely threaten the privacy of billions of users.
Utilizing very few resources, the researchers were able to perform practical crawling attacks on the popular messengers WhatsApp, Signal, and Telegram. The results of the experiments demonstrate that malicious users or hackers can collect sensitive data at a large scale and without noteworthy restrictions by querying contact discovery services for random phone numbers.
Attackers are enabled to build accurate behavior models
For the extensive study, the researchers queried 10% of all US mobile phone numbers for WhatsApp and 100% for …

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