Method and system for protecting a communication device from intrusion

(57) The invasion defense method for summary communications networks and a system realize address agility changed at both a schedule predetermined in a target host's (14) 's cyber-coordinates, and the time of invasion trial detection. The system is equipped with the management equipment (18) which maintains a series of tables which generated the cyber-coordinates of random sequence and included the set of the cyber-coordinates of the present and the next. In order to prevent unauthorized access, after these cyber-coordinates are applied to encryption processing, they are distributed to an authorized user (12).