war dialer n.

A cracking tool, a program that calls a given list or range of phone numbers and records those which answer with handshake tones (and so might be entry points to computer or telecommunications systems). Some of these programs have become quite sophisticated, and can now detect modem, fax, or PBX tones and log each one separately. The war dialer is one of the most important tools in the phreaker's kit. These programs evolved from early demon dialers.

--The Jargon File version 4.3.1, ed. ESR, autonoded by rescdsk.