War dialing

In cracking in the 1980s, the act of using a modem to dial every telephone number in a local area to find out where computers are available, then attacking them, trying to gain access by guessing passwords. See also war driving.

War dialing was made famous in the movie [War Games]?, in which the protangonists sets up his phone to call evey phone in another state until he reaches another modem, from which he can crack into more systems.