Can a Caller-ID signal be forged/altered ?
Since the signal is provided by the local Telco switch and the calling party’s line is not connected until after the phone is answered, generally the signal cannot be altered from the distant end. Manipulation would have to take place either at the switch or on the called party’s line. However, the foregoing applies only to a properly designed CNID unit. For instance the Motorola M145447 chip has a “power down” option that wakes the Chip up when the phone rings for just long enough to receive, process, and deliver the CNID signal after which it shuts down until the next call. Should this option be disabled, the chip will be in a “listen always” state and it is theoretically possible to “flood” a line making a vulnerable box record successive erroneous numbers. I have received a report of a device called “Presto Chango” that can transmit an extra ADSI modem tone after the call has been picked up that will cause a susceptible box to display the later information. It was also reported to
