As the use of intrusion detection systems increases, so too does the need for tools and methodologies for testing and evaluating them. The authors have developed a software platform that simulates intrusions and tests the effectiveness of intrusion detection systems. Their platform lets you create scripts that simulate both typical and suspicious activity, and has a record-and-replay feature that helps you create scripts quickly and easily. The platform supports the authors' testing methodology, which they outline here; both the platform and the testing methodology can be used to test and compare several different intrusion detection systems.