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Breach occurred 2025-10-23Verifiedsubstack.com
What happened
In October 2025, the publishing platform Substack suffered a data breach that was subsequently circulated more widely in February 2026. The breach exposed 663k account holder records containing email addresses along with publicly visible profile information from Substack accounts, such as publication names and bios. A subset of records also included phone numbers.
Data exposed
Frequently asked questions
The Substack data breach occurred on October 23, 2025. It was added to Have I Been Pwned's breach catalog on February 6, 2026.
663,121 accounts were affected by the Substack data breach, according to Have I Been Pwned's records.
The Substack breach exposed the following data types: Email addresses, Phone numbers.
Yes. Have I Been Pwned has verified the Substack breach, meaning there's confirmed evidence the exposed data is genuine and tied to real accounts.
Use KazaSec's free Email Breach Checker (/tools/breach-check) to check whether a specific email address has surfaced in the Substack breach, or any other known breach — the tool never stores what you search.
Our free Email Breach Checker tells you whether a specific email address has surfaced in this breach — or any other known breach — without ever storing what you search.
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