Besides writing programs to mimic telephone calling boxes, phone phreakers also created special programs called war dialers or demon dialers. War dialers are an old, but still effective, method for breaking into another computer.
War dialers work by hunting for telephone lines connected to a modem and a computer, which means that every person, corporation, and organization are potential targets. Because most people don't advertise their modem numbers, war dialers dial a range of phone numbers and keep track of any of the dialed numbers that respond with the familiar whine of a computer modem. A hacker can then use this list and dial each number individually to determine what type of computer he has reached and how he might be able to break in to it.
For example, many businesses have special phone lines that allow traveling employees to control their desktop computers with their laptop computers and special remote-control software, such as pcAnywhere, RapidRemote, or CarbonCopy. If a hacker finds this special phone number and uses a copy of the same remote-control software, guess what? With the right password, the hacker can take over the desktop computer too and then erase or copy all of its files.
Since war dialers can dial a number over and over again, they can also be used to harass people. Some of the more unusual harassment programs include a pager program that repeatedly dials a victim's pager number and randomly types in a phone number. Other phone harassment programs dial a single number over and over again at random intervals or play a computer-generated voice to insult a caller the moment he or she picks up the phone. (Just remember that with caller ID, available in most parts of the country, a victim can track your phone number, so it's not a good idea to call from any phone number that can be traced back to you.)