As the development of LAN (Local Area Network), the management of a LAN becomes more and more hard. So, some software had been built to solution the management problems, NetRoboCop was one of them.Computer in the LAN use MAC to communication each other. NetRoboCop though ARP (Address Resolution Protocol) to managing the LAN. It sends the wrong MAC data to the target computer. For example: Computer A need to communication to computer B, A will broadcast information to the LAN, and every computer in the LAN will receive the information. Computer B will send back information to A, it content computer B’s IP and MAC. The NetRoboCop will receive the information which A send too. And the NetRoboCop will send wrong information content B’s IP and a wrong MAC to A and when A received the ARP data information will refresh its ARP data. Computer a has a wrong MAC, and it can’t communication with B, the NetRoboCop achieve the goal.