In 2024, a collection called RockYou2024 exposed nearly 10 billion unique passwords compiled from years of data breaches. If you have used the same password across multiple sites — or used any common password at all — the chances are high that at least one of your passwords is already in a breach database.
The good news: you can check safely without revealing your password to anyone, using the k-Anonymity technique. Our free Password Leak Checker implements this exactly.
How Checking Works Without Exposing Your Password
The naive approach — sending your password to a server to check against a database — would be a serious security risk. The better approach uses a technique called k-Anonymity, developed by the Have I Been Pwned service:
- Your password is SHA-1 hashed entirely in your browser
- Only the first 5 characters of that hash are sent to the API
- The API returns all ~800 hash suffixes that begin with those 5 characters
- Your browser checks locally whether your full hash is in that list
The API never sees your actual password — or even enough of the hash to identify which specific password you looked up. This is the same technique used by Safari, Firefox and Chrome to check saved passwords against breach databases.
What the Results Mean
Found (with a count): Your exact password appears in breach databases. The count shows how many times it has appeared — a count of 3,000,000 means it is extremely common and must be changed immediately everywhere you use it.
Not found: The password has not appeared in any breach data that HIBP has collected. This does not mean it is a strong password — only that it has not been seen in a known breach. A password not in the breach database can still be guessable or weak.
What to Do If Your Password Was Leaked
1. Change it immediately on every site where you use it. Use a unique password for each site — if one gets breached, the others remain secure.
2. Generate a new strong password using our Password Generator. A 20-character random password with symbols is effectively uncrackable with current technology.
3. Enable two-factor authentication on all important accounts. Even if an attacker has your password, 2FA stops them.
4. Check your email address too using our Email Breach Checker — this shows which specific breaches your email address appeared in, what data was exposed and when.
The Passwords Most Commonly Found in Breaches
The most common passwords found in breach databases include: "123456" (over 35 million occurrences), "password" (over 9 million), "qwerty", "abc123", "iloveyou" and sports teams, names and years. Using any of these is functionally equivalent to having no password at all.
Check your passwords now at our free Password Leak Checker — no account needed, completely private.
