A modem (modulator-demodulator) is a hardware device that connects the digital signals from a computer to an analog telephone line. The sending modem modulates the data into a signal that is compatible with the phone line, and the receiving modem demodulates the signal back into digital data for the computer. This allows the signals to be transmitted longer distances than are normally possible.
Modem speeds at different years are shown below.
• 300 bps - 1960s through 1983
• 1200 bps - 1984 and 1985
• 9600 bps - 1991
• 56 Kbps - 1998
• ADSL (up to 8 megabits per second (Mbps)) – 1999
Modems normally respond to any call made to them when connected to an outside line and allow a connection. This may allow instant unsecured access to the network or the computers. If the modem is not really required, it should be disabled or removed from network work stations. If disabling the modem is not possible, it should be configured to prevent auto-answer.