A Simple WhatsApp Security Flaw Exposed 3.5 Billion Phone Numbers

Researchers at the University of Vienna extracted phone numbers for 3.5 billion WhatsApp users by systematically checking every possible number through the messaging service’s contact discovery feature. The technique yielded profile photos for 57% of those accounts and profile text for 29 percent. The researchers checked roughly 100 million numbers per hour using WhatsApp’s browser-based app.

The team warned Meta in April and deleted their data. The company implemented…