We shall discuss new problems of quantification/automation of anomaly-based Intrusion Detection System(IDS). We shall analyze effectiveness and weakness using our proposal method as an example, and derive new attack scenario. Development of anomaly-based IDS is necessary for correspondence to a high network attack, however, we shall show that it makes new different problems at the same time. In this paper, we shall discuss some attack scenario which makes invalidate our detection. As the result, we conclude that it is difficult to prevent such attacks technically, and security requirements for operation side become serious.