What is Credential stuffing?
When attackers take passwords leaked from one site and try them on your other accounts — which works if you reuse passwords.
After a company is breached, stolen email-and-password lists are traded online. Automated tools then try those combinations on hundreds of popular services. If you used the same password on the breached site and your email, both are now open. Unique passwords per site — via a password manager — make credential stuffing useless.