If your credentials have been leaked, change your password on that specific site and every other site where you used the same or a similar password.
Use trusted tools like Have I Been Pwned to see if your email address has appeared in a known breach or combo list.
Successful matches allow attackers to gain unauthorized access to accounts, which they may then use for financial theft, identity fraud, or reselling access.
Cybercriminals use these lists to launch large-scale automated attacks.
Setting up MFA provides a critical second layer of defense. Even if an attacker has your password, they will be blocked without the second verification code.
This is the primary use. Attackers feed the list into tools like OpenBullet to test the stolen credentials against other websites. It relies on the common habit of people reusing the same password across multiple platforms.
If your information is part of a leaked combo list, you should take immediate action to secure your digital identity.