Credential stuffing is a type of cyberattack where criminals use stolen usernames and passwords, often obtained from data breaches, to try and access accounts on other websites. Since many people reuse the same login details across multiple sites, attackers can automate the process of testing large numbers of stolen credentials, hoping to gain unauthorized access to user accounts. This technique can lead to account takeovers, identity theft, and financial loss for victims. Using unique passwords for each site and enabling two-factor authentication are effective defenses against credential stuffing.