In the security cracking scene of the 1980s, demon dialing was the act of using a Modem to dial every telephone number in a local area to find out where computers are available, then attempting to access them by guessing passwords.

Demon dialing was made famous in the movie WarGames , in which the protagonist sets up his phone to call every phone line in another state until he reaches another modem, from which he can crack into more systems. Since the movie s release, demon dialing has been popularly known in some circles as war dialing, in tribute to the movie.

Similar to demon dialing is a port scan under TCP/IP, which dials every Transmission Control Protocol computer port of every IP address to find out what services are available, then gaining access to them by guessing passwords or by exploiting vulnerabilities in software that runs with elevated privileges. Unlike demon dialing, however, port scans will generally not disturb a human being when it tries an IP address that isn t up.