What was exposed, when it happened, and which databases confirm it.
- accounts
- 1,280,604
- Breached
- October 23, 2025
- Last Update
- February 6, 2026
Were you caught in this breach?
Search your email, phone number or username against every record CheckLeaked indexes.
Your address never leaves this page: it is hashed in your browser and only a short fragment of that hash is sent.
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.
Compromised Info
- Email addresses
- Phone numbers
Attestation
Four independent databases catalog this breach and they do not always agree. Each lane below is one source’s own count.
Sources & Link Methods
- LeakCheck— linked via automatic string matching
- HIBP
FAQ
What was leaked in the Substack breach?
The Substack breach exposed: Email addresses and Phone numbers.
When did the Substack breach happen?
The Substack breach was disclosed on October 23, 2025 and affected 1,280,604 records.
Am I affected by the Substack breach?
Search your email, phone or username at checkleaked.cc to find out whether your data appears in the Substack leak.