Patent ID: 7552478

Claim:
A network unauthorized access preventing system for preventing an unauthorized apparatus, which is not authorized to access a network, from accessing one or more information processing apparatuses connected to said network, said system comprising: a network unauthorized access preventing apparatus which sends a response packet containing a false physical address as a physical address of said information processing apparatus to said unauthorized apparatus, after said information processing apparatus sends a correct response packet to said unauthorized apparatus in response to a request which is broadcast from said unauthorized apparatus for knowing a physical address, wherein said network unauthorized access preventing apparatus comprises: an authorization list storage unit which stores a physical address of an information processing apparatus which is authorized to access said network; collects all packets transmitted via said network in an indiscriminate reception mode; determines whether or not a physical address of a packet sender which is contained in a collected packet is registered in said authorization list storage unit, and detects the packet sender of this packet as said unauthorized apparatus in a case where the physical address is not registered in said authorization list storage unit; sets a predetermined designation time when receiving the request; in a case where the correct response packet is sent to said unauthorized apparatus from said information processing apparatus regardless of whether it is before or after the designation time elapses, receives the correct response packet and sends the response packet containing the false physical address to said unauthorized apparatus immediately after receiving the correct response packet; and in a case where not receiving the correct response packet before the designation time elapses, sends the response packet containing the false physical address to said unauthorized apparatus when the designation time elapses.