Network connected device protection

A network controller comprising:

• a security signal generator for periodically providing a security signal on at least one port of said network, said port performing normal data transfers between said periods when said security signal is provided;
• a security sensor connected to said port for sensing during one period, a first feedback signal from said port, said first feedback signal being a response by a normal impedance of a terminal device to said security signal without regard to operation of said terminal device and providing a first security data during said one period, said security sensor sensing during another period, a second feedback signal when a terminal device is not connected to said port, and providing a second security data during said another period;
• security logic connected to said sensor and responsive to said sensor for comparing said first security data with said second security data in order to determine if said terminal device has been removed from said port and to determine if said terminal device has been added to said port;
• and
• an alarm connected to said security logic and responsive to said security logic for alerting an operator when said security logic has determined that said terminal device has been removed from said port and when said security logic has determined that said terminal device has been added to said port.