pam-abl used for DoS attack.

     Pam_abl or libpam-abl is a pam module used to black list users or IP addresses that repeatedly fail authentication.  It serves the same function as fail2ban but has a flaw that it can be used to deny service to a user by repeatedly trying passwords for that user from different IP addresses.  It was used to deny a number of customers from using webmail and in the process of troubleshooting I also broke the mount point for mail used by ubuntu, so both webmail and ubuntu were inaccessible for a while.  This module has been disabled since it can be abused this way and is redundant as it serves the same function as fail2ban.