Analyses were made on the security threats of present immune IDS schemes and the useful metaphor of biological immune system considering its application in the study of IDS. In light of the system flaws arising from the transfer of disease-causing mechanisms of biological immune system into IDS, a hybrid IDS scheme based on biological immunology and mobile agent was presented. The scheme precludes the security problems by utilizing the useful metaphors of biological immunity and the prominent characteristics of mobile agent, and is characterized by parallel operating, stability, adaptability and robustness. Further detailed analyses also justify its brevity, security, high efficiency, and thus considerable improvement on system overheads regarding software and hardware application