Hey There! You Are Using WhatsApp: Enumerating Three Billion Accounts for Security and Privacy

WhatsApp, with 3.5 billion active accounts as of early 2025, is the world's largest instant messaging platform. Given its massive user base, WhatsApp plays a critical role in global communication. To initiate conversations, users must first discover whether their contacts are registered on the...

A Simple WhatsApp Security Flaw Exposed 3.5 Billion Phone Numbers

By plugging tens of billions of phone numbers into WhatsApp’s contact discovery tool, researchers found “the most extensive exposure of phone numbers” ever—along with profile photos and more...

On the macOS Keychain Attack, Signal’s New Contact Service, the Deloitte Hack, and More

Mike Mimoso and Chris Brook recap the news of the week, including the macOS Keychain attack, Signal’s new private contact discovery service, the Deloitte hack, and a handful of mobile stock trading app vulnerabilities. Download: ThreatpostNewsWrapSeptember292017.mp3 Music by Chris Gonsalves Show...

Signal Testing New Private Contact Discovery Service

Open Whisper Systems, the company behind the encrypted messaging app Signal, is testing a new private contact discovery service that in theory will allow the app to determine if a user has Signal contacts in their address book but forbid its servers from accessing the users’ address book. Moxie...