How data breach checkers work, and what they can’t tell you
2 min read · Updated October 15, 2026
Breach checkers collect records from known data breaches, store them in searchable form and compare your email address against that collection. A match means your address appeared in a known incident. They cannot cover every breach, so a clean result lowers risk but cannot prove you are safe.
Where the data comes from
Breached data surfaces in several ways: companies disclose incidents, researchers find exposed databases, and stolen data is posted or traded publicly. Breach services collect and organise records from these sources so that people can search them.
What happens when you search
You submit an email address. The service looks for that address in its dataset and returns matches, usually with the name of the breached service and the date. Some tools show only a yes or no, others list the incidents and the types of data exposed.
Find out if your email is in a known breach
Run the free Leakill check. No password needed, no signup, and you see the result in seconds.
Why results differ between tools
Each tool curates its own sources, so one may know about an incident that another does not. Some focus on large, verified breaches while others include smaller leaks and combined lists. That is why two checkers can give different answers about the same address, and why many security professionals suggest checking with more than one source.
Limits worth knowing
- ✓Unreported or undiscovered breaches are invisible to every checker.
- ✓A match shows exposure, not misuse.
- ✓A clean result applies to the data the tool has, not the entire internet.
- ✓Some breach data never lists the email at all, so you could be affected without a match.
Frequently asked questions
Does a breach checker know my passwords?+
A responsible one does not ask you for passwords. Some services can tell you that a password in a breach was exposed, without you entering your current one.
Why does my email show a breach for a service I never used?+
Data brokers, mailing lists and combined leaks include addresses that were scraped or bought, so you may appear without ever creating an account.
How current are breach databases?+
They update as new incidents are found, which can be days, months or years after the breach itself.
Stop guessing. Check your email in seconds.
The free Leakill check looks for your email address in known breach records and tells you whether it was exposed. If it was, an optional detailed report lists the incidents, dates, sources, the kinds of data involved and practical next steps. It is a one-off report, not a subscription.
A breach match is a warning signal, not proof that someone has access to your account today. No public database covers every breach, so a clean result lowers risk without guaranteeing safety.