T 5.37 Determining access codes

Almost all modern answering machines are equipped with a number of functions in addition to the recording of messages. Typical examples are: remote inquiry, call redirection, room monitoring, or telecontrol of connected electrical devices. These functions can be controlled remotely while the answering machine is being called (in the case of dial pulsing with an additional remote control device, in the case of multi-frequency dialling system directly with the telephone keys). The use of this remote inquiry and control feature is generally protected by a security code (code number, PIN). This access code is also transmitted from the remote inquiry device to the answering machine with tones of different frequencies.

If third parties were able to find out that access code, it would be possible for them to influence the answering machine via the remote control as if it was their own answering machine. The consequential damage would depend on whether a third party monitored sensitive messages or misused other features.

Example:

According to recent reports, the access codes of some answering machines have been increasingly cracked by using a standard PC and a connected modem to try out all possible number combinations within a very short time.