# Data Breach

An incident in which sensitive, protected, or confidential data is accessed, copied, or disclosed without authorization.

A **data breach[↗](/data-breach)** is an incident in which sensitive, protected, or confidential data is accessed, copied, or disclosed by someone who wasn't authorized to see it, whether through hacking, a lost device, an insider misusing access, or a simple misconfiguration that left data publicly exposed. Breaches can involve anything from a handful of records to hundreds of millions of user accounts.

When a service you use is breached, the practical risk depends on what data was exposed: a leaked password should be changed everywhere it was reused, while exposed personal information (like a national ID number) may carry longer-term identity theft[↗](/identity-theft) risk. Using unique passwords per account and checking a breach-notification service periodically are two of the most effective ways to limit the damage a breach can do to you personally.