Was your data in the Substack breach?
Check whether your email address was in it
Check my exposureFree. No password — we email you a six-digit code. This breach and every other one your address appears in.
Substack (substack.com) suffered a data breach in 2025 that exposed around 663,121 accounts. If you had an account, some of your personal data may be circulating in leaked databases. The fastest way to know is to check your own email — free, in about 30 seconds, no password required.
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.
Breach record from Have I Been Pwned, CC BY 4.0. Risk analysis by Nullivo.
What was exposed, and why it matters
Not all breaches carry the same risk — what matters is which fields leaked. Here is what the Substack breach exposed and what each item actually enables:
What to do if you were affected
These steps are ordered for this specific breach — the most urgent action given what leaked comes first.
- Phone numbers
Move two-factor authentication off SMS to an authenticator app or passkey, and add a port-out PIN with your mobile provider. - Email addresses
Treat any message referencing this service with suspicion, and never act on links in unexpected emails. - Confirm you were actually in it
Run a free scan before you spend time on the steps above.
How urgent is this now?
This breach is recent, so the data is actively traded and the risk is at its highest right now.
Remember: a breach can’t be “un-leaked” — once a database is out, it exists in countless copies. The goal is to make the leaked data useless: change what can be changed, lock down what can’t, and remove what has been republished.
Frequently asked questions
What data was exposed in the Substack breach?
The Substack breach exposed phone numbers, email addresses. Enables SIM-swap attacks (hijacking your number to intercept SMS codes), smishing, and voice scams that appear to come from your bank.
How many people were affected by the Substack breach?
Around 663,121 accounts were exposed, making it a mid-sized breach.
What should I do if I had a Substack account?
Move two-factor authentication off SMS to an authenticator app or passkey, and add a port-out PIN with your mobile provider. You can check whether your own email appears in this breach with a free Nullivo scan — no password required.
Breaches that exposed similar data
If the Substack breach affected you, these breaches exposed comparable information — worth checking too, since leaked datasets are routinely combined.