Patent ID: 8505072

Claim:
A network device that restricts access to predetermined information held therein, the network device comprising: an acquisition unit that communicates with one or more local devices that are in a communicable state within a same local area network as the network device, and acquires one or more identification information pieces corresponding thereto; a calculation unit that, for each local device whose identification information piece has been acquired, calculates an index value of the local device based on a past communication therewith, the index value being used for judging whether to restrict the access and for estimating an existence probability of the local device, and the existence probability being a ratio at which the local device exists in the communicable state; a holding unit that, for each local device whose identification information piece was acquired before a given time point, holds the identification information piece of the local device and the index value thereof calculated by the calculation unit; a difference specifying unit that specifies a difference between (i) one or more identification information pieces acquired after the given time point and (ii) the one or more identification information pieces acquired before the given time point, so as to specify one or more of the local devices as the difference; and a judgment unit that judges whether to restrict the access based on the index value of each local device specified as the difference: wherein the difference specifying unit specifies the one or more of the local devices as the difference by comparing the one or more identification information pieces acquired after the Riven time point by the acquisition unit, with one or more identification information pieces that were acquired during a predetermined time period that ends at the given time point.