IM(Instant Messaging) is used widely

which is an avenue for the propagation of IM malicious codes.To restrain IM malicious codes

we proposed a collaborative defending scheme based on social computing.Users can obtain experience after they browse through web pages and run malicious codes.Based on the trust between a user and his friends

through social computing

the experience and the checking results about IM malicious codes from different antivirus softwares on hosts are collected to result in collective intelligence.The platform used in the scheme is the social network formed by IM tool.Dynamic trusts on friends are calculated according to massages from friends.The scheme is a distributed system which is implemented in clients.Users collaborate with their friends to slow down the propagation of IM malicious codes.The experiments show all nodes in the social network are immune at last in the case when most users accept the warning

and the defending capacity of the whole social network is enhanced.