Substack, the hugely popular online content platform with 50 million active subscribers, has confirmed it has been hacked.

The hacker claims to have stolen nearly 700,000 Substack user records, including email addresses and phone numbers.

Substack said that customer data was accessed in October 2025, but wasn't discovered until early February.

Substack confirms a major data breach exposing user emails and phone numbers. What’s behind the breach, and what’s next?

Newsletter platform Substack has confirmed it suffered a security incident, leading to the compromise of users’ email addresses and phone numbers. Chris Best, the CEO of Substack, notified users of ...

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