1. A method for detecting unfair use comprising: recording a plurality of operation feature quantities which are calculated from an operation log of a 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 a terminal device; calculating a plurality of operation feature quantities from the operation log; and calculating similarity between the calculated plurality of operation feature quantities and 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 unfair use of the terminal device.