A software called War Dialer IV
War Dialing, Scanning or Janning is a phrase used by phone phreaks and refers to systematically calling all the numbers in a specific prefix, usually to identify any computer that was connected to a modem. This could be done manually or by a computer program. The program would call each number, if no one answered or if a person would answer then the program would hang up and dial the next number. If another computer would answer then the program would make a note of that number, ether by saving it in a text file or printing it out. After a few hours you would have a list of any computer in the area hooked up to a modem. Phone phreaks could then try to hack into these computers.
Many people will remember seeing war dialing being used in the film War Games.