Credential Stuffing: Hackers take leaked username/password pairs from one breach and try them on hundreds of other sites automatically. If you reuse passwords, many accounts fall at once.

Phishing Amplification: If you're tricked into entering your password on a fake site, attackers immediately try it on your email, bank, and other services.

Solution: Use a unique, strong password for every account. Use a password manager so you don't have to remember them.