1. A method for detecting unfair use of a terminal device, comprising: recording a plurality of operation feature quantities of a user, which are determined from an operation log of the user, and weights for the plurality of operation feature quantities of the user, which are calculated by using a plurality of operation feature quantities of other users; obtaining an operation log of the terminal device; determining a plurality of operation feature quantities of the terminal device from the operation log of the terminal device; and calculating similarity between (i) the determined plurality of operation feature quantities of the terminal device and (ii) the recorded plurality of operation feature quantities of the user, by using the recorded weights for the plurality of operation feature quantities of the user, and detecting the unfair use of the terminal device, wherein the operation feature quantities are determined by using at least one of acceleration information, position information of the terminal device, or operation information of a touch panel in the terminal device.