Securing a new Drupal site is critical because Drupal installations are insecure by default (functionality is considering more important than security in a default install).
- Restrict user registration
- Remove error messages
- Enable SSL for logins (http://drupal.org/project/securepages)
- Enable private files and move the default file directory out of the webserver's document root path
- Enable a password policy (http://drupal.org/project/password_policy)
- Modify the theme to remove usernames from posts