PROBLEM TO BE SOLVED: To easily and exactly discriminate whether a client is illegal or not.;SOLUTION: History information stored in access log DB 26 is referred to. The number of processing request times and the number of authentication failing times are summed up for each client 10. An authentication failing ratio showing the ratio of the number of authentication failing times, which is occupied in the number of processing requesting times, is calculated for each client 10. A suspicious index showing the suspiciousness of the client 10 is calculated for each client 10 by using the number of authentication failing times and the authentication failing ratio. It is judged whether the clients 10 are illegal or not based on the calculated suspicious index.;COPYRIGHT: (C)2002,JPO
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