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Make sure that incoming modems automatically log out the user if the telephone call is interrupted .
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Make sure that incoming modems automatically hang up on an incoming call if the caller logs out or if the caller's login process is killed .
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Make sure that outgoing modems hang up on the outgoing call if the tip or cu programs are exited.
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Make sure that the tip or cu programs automatically exit if the user is logged out of the remote machine or if the telephone call is interrupted.
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Make sure that there is no way for the local user to reprogram the modem. Disable any remote configuration or testing features.
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Greet incoming connections with an appropriate banner.
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Do not install call-forwarding on any of your incoming lines.
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Consider getting CALLER-ID/ANI to trace incoming calls automatically. Log the numbers that call your system.
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Physically protect the modems and phone lines.
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Disable third-party billing and call-forwarding on your modem lines. Don't order long-distance service on modem lines that don't need it.
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Consider getting leased lines, callback modems, or telephone firewalls.
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Consider using separate callout telephone lines with no dial-in capability for callback schemes.
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Check permissions on all associated devices and configuration files.
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Consider using encrypting modems with fixed keys to guard against unauthorized use or eavesdropping.
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Use a telephone scanner to search for unauthorized modems.
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Consider changing your modem phone numbers periodically.