Substack data breach
From Breaches, in the HARD wiki · Updated
This article is about the October 2025 breach of Substack. For every breach, see Breaches.
The Substack data breach exposed 663,121 accounts from substack.com in October 2025. The data taken includes email addresses and phone numbers.[1]
Have I Been Pwned verified it and added it to its search on 6 Feb 2026, 3 months later. It is the 456th largest of the 618 breaches in HARD’s list.
What was exposed
Substack’s breach included 2 kinds of data. What each lets criminals do:
| Data | What it’s used for |
|---|---|
| Email addresses | Expect scam emails that name the company to look genuine. |
| Phone numbers | Expect scam texts and calls, and a higher risk of someone moving your number to their SIM. |
What to do
- Check whether you’re in it.Search your email address on Have I Been Pwned. It tells you which breaches it appears in, Substack among them, without showing the data.
- Distrust messages that mention Substack.Scammers use breach data to sound genuine. Don’t click links in emails or texts about the breach; go to the site yourself.
- Put a PIN on your phone account.Ask your mobile provider for a port-out PIN, so no one can move your number to their SIM.
Timeline
- : the breach, as best it can be dated.
- : Have I Been Pwned verifies the data and adds it to its search, 3 months later.
Similar breaches
Breaches that leaked the same kinds of data, closest in time:
- Canadian Tire, October 2025, 38 million accounts
- Vietnam Airlines, June 2025, 7.3 million accounts
- Bouygues Telecom, August 2025, 5.7 million accounts
- Scholastic, January 2025, 4.2 million accounts
- WIRED, September 2025, 2.4 million accounts
- Allianz Life, July 2025, 1.1 million accounts
See Breaches for all 618, and Updates for keeping your devices patched.
References
- ^ Troy Hunt. “Substack”, Have I Been Pwned, added 6 Feb 2026. Breach data licensed CC BY 4.0.
External links
- Have I Been Pwned, to check your email address
- substack.com, Substack’s website