Source : Free On-Line Dictionary of Computing

carrier scanner
     
         (Or "wardialer") A program which uses a {modem} to
        dial a series of phone numbers (say, from 770-0000 to
        770-9999), and keeps a log of what phone numbers answer with a
        modem {carrier}.  The results of such a search were generally
        used by people looking to engage in {random} mischief in
        {random} machines.
     
        Since the 1980s, wardialers have generally fallen into disuse,
        partly because of easily available "{caller ID}" technology,
        partly because fax machines are now in wide use and would
        often be logged as a {carrier} by a wardialer, and partly
        because there are so many new and more interesting venues for
        computerised mischief these days.
     
        (1997-03-16)