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

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

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

"We're moving quickly," Farrah Storr, head of international at Substack, tells THR after hiring Mark Swierszcz as its new Canadian head of partnerships, with more country hires in the works worldwide.

Substack won't share official numbers, but it seems like a pretty significant data breach.

Substack states that the security flaw has now been fixed and that a full investigation is underway. There are currently no ...

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