Data breach

A data breach happens when a service’s user data falls into the wrong hands through an attack or a security flaw, usually including emails, usernames and passwords. Criminals then try those combinations on other sites ( credential stuffing ✕ Credential stuffing automatically tries stolen emails and passwords across many sites at once, exploiting the fact that people reuse passwords. More in the glossary → ), which is why a single reused password can open several accounts. The best defense is a different, strong password for each service —easy with a manager— plus two-factor authentication. It is worth checking whether your email appears in known breaches and changing the affected passwords right away. Many managers alert you when one of your passwords has been compromised. Which ones offer that alert is covered in the best password managers comparison.