An apparatus and method are disclosed that enables detecting the spoofing of a telephone number. To validate the identity of a calling terminal, some techniques in the prior art rely on exchanging data that only the legitimate calling system and the called system know about. In contrast, the illustrative embodiment of the present invention validates the identity of the calling terminal by assessing characteristics other than the calling terminal's telephone number, such as the telephone type and the signaling protocol. By using characteristics other than telephone number to validate the identity, the data-processing system of the illustrative embodiment makes it more difficult to spoof a legitimate telephone's number.