Substack data breach: 663K accounts exposed
Severity: medium · Patch status: no-fix-needed · Since 2026-02-06
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. Exposed data: email addresses, phone numbers. The breach dates from Oct 23, 2025; Have I Been Pwned loaded it on Feb 6, 2026.
What to do
- If you had a Substack account, change its password and the password of any other account that reused it.
- Turn on multi-factor authentication wherever it is offered.
- Check whether your addresses are in this breach at https://haveibeenpwned.com.
- Expect targeted phishing that quotes the leaked details; verify any unexpected contact out of band.
Sources
All live incidents on Threat Watch