Substack — data breach (Substack)

Domain: substack.com · Accounts affected: 663,121 · Data exposed: Email addresses, Phone numbers · Verified breach — 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.