Grid is a kind of distributed computing environment, which allows large scale resource sharing and system integration. Grid computing is a kind of important information technology which enables resource sharing globally to solve the large scale problem. The services and resources in Grid are heterogeneous and dynamic, and they also belong to different domains. To combat attackers, Intrusion-Detection Systems (IDSs) can offer additional security measures for these environments by investigating configurations, logs, network traffic, and user actions to identify typical attack behavior. However, an IDS must be distributed to work in a grid computing environment. It must monitor each node and, when an attack occurs, alert other nodes in the environment.