With the widespread use of the Internet and intranets, it is becoming more and more important for us to protect information and intellectual property rights of corporations. This paper describes the shortcomings of traditional security technologies and presents an information protection system for intranets. The system includes four components that are data collection, policy management, data analysis and data presentation. The system uses the Latent Semantic Indexing to analyze the information flowing between the intranet and public networks. The system detects and stops information which is not permitted to be transmitted. Experimental results show that the system carries out the analysis accurately as well as efficiently. The system provides an effective solution to protecting information in an intranet environment.