Consider using an unpublished number rather than a toll free number for remote access and limit the number of employees with access to the remote number. Use a voice recording or silent prompt rather than a tone prompt for remote access. When maintenance ports are not in use, deny access. Infiltrating and reconfiguring the maintenance port of a PBX is a common method for fraud. CPE systems often include maintenance and administration ports which can control not only telecommunications but also office environmental features such as lighting and climate.
Experienced hackers know how to activate disabled or dormant ports.
Any ports not in use should be physically disconnected. Always activate ports manually. Have vendors do on-site maintenance. Physically disconnect remote access lines to your system administration ports. If available, use multiple levels of security on maintenance ports.