How to Tell If Your Password Was Leaked

There is a good chance at least one of your passwords is already sitting in a breach database somewhere. Billions of leaked credentials circulate online, harvested from years of website breaches. The good news is that you can check whether your passwords have leaked — safely, without handing them over to anyone — and take action if they have.

How password leaks happen

When a website is breached, attackers often walk away with its user database: email addresses and passwords (sometimes poorly protected). These dumps get traded and aggregated into massive collections. If you ever used a password on a site that was later breached, that password may be in one of these collections, paired with your email. Attackers then try those pairs on other sites — an attack called credential stuffing. See what is credential stuffing.

How to check safely

The key concern when checking is: how do you test a password without revealing it? The answer is a clever technique called k-anonymity, used by reputable breach-checking services.

Here is the idea: your password is hashed (turned into a fixed-length code), and only the first few characters of that hash are sent to the service. The service returns all leaked hashes starting with those characters, and your device checks the rest locally. The full password — and even its full hash — never leaves your device. You learn whether it appears in known breaches without exposing it.

Our password leak checker uses exactly this method. You can also check whether your email address has appeared in known breaches through public breach-notification services.

Signs your password may be compromised

Beyond proactively checking, watch for these warning signs:

• A service emails you that it suffered a data breach.
• You receive password-reset emails you did not request.
• You get login alerts from unfamiliar locations or devices.
• Friends report spam or strange messages from your account.

Any of these warrants immediate action.

What to do if a password leaked

1. Change it immediately on the affected account. Generate a fresh unique password with the secure password generator.
2. Change it anywhere you reused it. This is the big one — if the leaked password was reused, every account sharing it is at risk. See how to stop reusing passwords.
3. Enable two-factor authentication so a leaked password alone is not enough. See what is two-factor authentication.
4. Watch for follow-on attacks like phishing emails referencing the breach.

For a full walkthrough, see what to do after a data breach.

Prevent the next leak from hurting you

You cannot stop websites from being breached, but you can make breaches harmless. The trick is uniqueness: if every account has its own password, a leak from one site exposes only that one account, never the others. A password manager makes this realistic. On a Mac, Passlock stores unique passwords offline in the Keychain, so when (not if) some site you use is breached, the damage stops at that single account.

Checking for leaks is not paranoia — it is basic hygiene in an era of constant breaches. Check your important passwords today, fix any that show up, and make sure every account has its own.