This module enables you to prevent existing users from logging in to your Drupal site unless they know the secret key to add to the end of the ?q=user login form page.
The Login Disable module does not correctly prevent a user with a disabled login from logging in, allowing those users to by-pass the protection offered by the module.
This vulnerability is mitigated by the fact that an attacker must already have a user account to log in. This bug therefore allows users to log in even if their login is disabled.