Breached-password screening is a defensive check that compares a chosen password against databases of passwords exposed in previous leaks. If the password appears in a known breach list, the system rejects it or forces the user to pick another. This helps stop two common attack paths: password reuse, where one leaked secret unlocks multiple accounts, and password spraying, where attackers try commonly reused passwords across many users.
In practice, screening is used during account creation, password changes, and sometimes login risk checks. It is especially important in single sign-on environments, where one weak credential can open access to many applications. Screening does not make a password strong by itself, and it does not replace multi-factor authentication, but it removes one of the easiest ways attackers gain a foothold. Good implementations compare only the password material needed to test against breach data and avoid exposing the user’s secret.