Reused credentials are the same username and password, or the same login session, used on more than one service. This is risky because a breach at one site can give attackers a working account on another site if the victim reused the same password or identity provider access.
In cyber security, reused credentials are a common path for account takeover, ransomware access, and lateral movement. Attackers test stolen logins against email, VPN, cloud apps, and admin portals, often with automated tools. Defenders reduce this risk with unique passwords, password managers, multi-factor authentication, single sign-on controls, and alerts for credential stuffing or unusual login patterns. When a victim listing appears, teams should verify whether reused credentials or exposed remote access could explain the claim and close any shared access paths.