This article is focused on analyzing the key technologies of new malicious code and corresponding defensive measures in the large-scale communication networks.Based on description of the concepts and development of the malicious code,the article introduces the anti-analysis technology,splitting and inserting technology,hiding technology,polymorph virus technology,and auto production technology of the malicious code trends with intelligence,diversity and integration.Following that,it summarizes the security vulnerabilities of communication networks from four related layers aspects,according to the mechanisms of malicious code in the communication networks.Finally,it proposes rapid response disposition of malicious code attacks from four correlated steps: building up the network node monitoring system,suspicious code feature automation analysis and extraction,rapid active malicious code response technique for unknown malicious code,and malicious code attack immunity technique.As a result,it actively defenses against the unknown malicious code attacks and enhances the security performance of communication networks.