A war dialer is a computer program used to identify the phone numbers that can successfully make a connection with a computer modem. The program automatically dials a defined range of phone numbers and logs and enters in a database those numbers that successfully connect to the modem. Some programs can also identify the particular operating system running in the computer and may also conduct automated penetration testing. In such cases, the war dialer runs through a predetermined list of common user names and passwords in an attempt to gain access to the system.
A war dialer, usually obtained as freeware, is typically used by a hacker to identify potential targets. If the program does not provide automated penetration testing, the intruder attempts to hack a modem with unprotected log-ins or easily cracked passwords. Commercial war dialers, also known as modem scanners, are also used by system administrators, to identify unauthorized modems on an enterprise network. Such modems can provide easy access to a company's intranet.