Abstract: Based on the analysis of communication mechanism of mainstream instant messenger software, summary of the various instant messengers' transmission protocol of texts, a standard monitor system for instant messenger-IMSMMS was designed and realized. Through session association, IMSMMS can intercept the sender and the receiver of the message effectively. IMSMMS not only extracts the text message of the mainstream instant messengers (such as MSN,Fction,Yahoo! Messenger etc.)for multiple versions, but also extracts the text message between two different kinds of software: MSN and Yahoo！ Messenger. Through setting the sensitive words, the system can filter out messages that contain sensitive words. The experiment results show that when the IM text message packets though the gateway is less than 1000 per second, IMSMMS only has a rate of missing packet less than 0.21%. The result indicates that IMSMMS can meet the network security requirements of small scale Intranet effectively.

Key words: Instant messenger, Session association, Protocol analysis, Monitor management