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WhatsApp Security Flaw Exposes Data of 3.5 Billion Users

11/26/2025

Summary

Story summary

Researchers from the University of Vienna found a security flaw in WhatsApp that exposed 3.5 billion users' phone numbers, profile photos, and 'About' text.
The flaw originated in the app's contact discovery mechanism, enabling attackers to check up to 100 million numbers per hour.
Meta implemented protections after researchers disclosed findings in April 2025, and the study notes duplicated encryption keys while warning against using phone numbers as primary identifiers.

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Story summary

Researchers from the University of Vienna found a security flaw in WhatsApp that exposed 3.5 billion users' phone numbers, profile photos, and 'About' text.
The flaw originated in the app's contact discovery mechanism, enabling attackers to check up to 100 million numbers per hour.
Meta implemented protections after researchers disclosed findings in April 2025, and the study notes duplicated encryption keys while warning against using phone numbers as primary identifiers.