Password blacklists are applied to prevent users from choosing passwords that are easily guessed or are well known and could lead to unauthorized access by malicious parties. Password blacklists are deployed as an additional layer of security, usually in addition to a password policy, which sets the requirements of the password length and/or character complexity. This is because there are a significant number of password combinations that fulfill many password policies but are still easily guessed (i.e., Password123, Qwerty123).