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Response snapshot Oct 26, 2026, 21:37 UTC

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Disclosed incidenthibp-substack

Substack breach: 663,121 accounts exposed

In October 2025, the publishing platform Substack suffered a data breach that was subsequently circulated more widely in February 2026.

At a glance

Sources
1 source

What to do

If you or your organization used this service, change reused passwords, watch for phishing that uses the exposed data, and check the disclosure for the organization's guidance.

Read Have I Been Pwned: Substack (opens a new tab)

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.

Related technology

Sources

  1. Primary source

    Have I Been Pwned: Substack (opens a new tab)

    Verified breach loaded into Have I Been Pwned: account count, exposed data types, and dates.

    Published Checked

  2. Primary source

    Have I Been Pwned breach API (opens a new tab)

    The breach list that supplied this entry.

    Published Date not suppliedChecked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, February 6). Substack breach: 663,121 accounts exposed. https://kevwire.com/record/hibp-substack

MLA

"Substack breach: 663,121 accounts exposed." KEVWire, 6 Feb. 2026, kevwire.com/record/hibp-substack.

Chicago

KEVWire. "Substack breach: 663,121 accounts exposed." Last modified February 6, 2026. https://kevwire.com/record/hibp-substack.

Evidence summary (plain text)

Substack breach: 663,121 accounts exposed (Feb 6, 2026).
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.
Sources:
Have I Been Pwned: Substack: https://haveibeenpwned.com/Breach/Substack
Have I Been Pwned breach API: https://haveibeenpwned.com/api/v3/breaches
Record ID: hibp-substack.
Record origin: Ingested record.
AI evidence: Not assessed.
About this data

This record was ingested from a data source. Retrieved: Oct 26, 2026, 21:25 UTC. Ingestion is not an independent editorial investigation.

Verified by Have I Been Pwned. Breach date: 2025-10-23; loaded 2026-02-06. Exposed data: Email addresses, Phone numbers. Counts are accounts in the loaded data, not necessarily distinct people.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

Record JSON

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