Network management apparatus, a network system, a network management method and program

Prevent unauthorized access to the other devices from the terminal that is invaded by a malicious user. Network management device is a network management device connected via the communication device and the terminal, on the network to which the network management device manages, be identification information for identifying the terminal, the network management apparatus is a regular the regular information generating means for generating a normal identification information managed as information, an identification information of a different costume is the identification information of said normal, the identification information of costume which can not be used as it is to communicate with another terminal comprising a costume information generating means for generating for the identification information of the identification information and the costume of the normal, and management means for managing in association with the identification information of the costume, and registration means for registering the terminal.