Modem and dialup security is a topic that many of today's security practitioners rarely consider, yet one that remains of critical importance even in this age of Internet-based communications. If you use modems with your Unix system, it is vital that you ensure that the cables are correct and that the modem is properly configured. Remember: even a modem that appears to be working properly can cause a grave security threat if it was improperly set up. If you aren't sure you are running any modems, conduct a visual inspection of your computers to be sure. Then check your elevators, your HVAC systems, and your burglar alarms. These days, lots of systems have modems. You can't be too careful!