The presence of unsecured or mis-configured modems attached to computers on the network can undermine a well thought-out security plan. Persons unaware of the risks may set up modems on their computers that can be accessed with either non password or an easily guessed password. These modems are then vulnerable to computer criminals who “war dial,” or call numbers systematically until they find a phone number that connects to an unsecured dialup.
If a computer with an unsecured modem is connected to our network, anyone with a little computer skill and malicious intent can use that unsecured modem as a “back door” into our network. Firewalls don’t protect a network against this type of attack because the intruder comes in over phone lines, rather than over the Internet, bypassing firewalls.