Synthient Credential Stuffing Threat Data data breach

Breach date: 2025-04-11. Added to this index: 2025-11-06. Accounts affected: about 2.0B. Domain: not listed.

What happened

During 2025, the threat-intelligence firm Synthient aggregated 2 billion unique email addresses disclosed in credential-stuffing lists found across multiple malicious internet sources. Comprised of email addresses and passwords from previous data breaches, these lists are used by attackers to compromise other, unrelated accounts of victims who have reused their passwords. The data also included 1.3 billion unique passwords, which are now searchable in Pwned Passwords. Working to turn breached data into awareness, Synthient partnered with HIBP to help victims of cybercrime understand their exposure.

Breach data sourced from Have I Been Pwned, used under CC BY 4.0. Additional breach metadata provided by XposedOrNot. DataExposed is an independent service and is not affiliated with or endorsed by either.

What was exposed

  • Email addresses: The email address you used to register or log in. It is the most common field in breaches because it doubles as your username on most sites.
  • Passwords: The secret you use to sign in, stored by the breached service either in plain text, in a scrambled form called a hash, or encrypted. How it was stored decides how quickly it can be recovered.

What to do now

  1. Check whether your own address is in this dataset with the free email breach check.
  2. Change the password on this service and every other site where you used the same password.
  3. Turn on two-factor authentication on your email account first, because it is the reset path for everything else.
  4. Treat calls and messages that quote real details about you as hostile until you verify them another way.

Frequently asked questions

What data was leaked in the Synthient Credential Stuffing Threat Data breach?

The Synthient Credential Stuffing Threat Data breach exposed Email addresses, Passwords. About 2.0B accounts were affected.

Was I affected by the Synthient Credential Stuffing Threat Data breach?

Run the free email breach check with the address you used on that service. It will tell you whether your address appears in this dataset.

What should I do about the Synthient Credential Stuffing Threat Data breach?

Change the password on that account and everywhere you reused it, then turn on two-factor authentication. Passwords from this breach are traded and tried automatically against other sites.

Next steps