Emerging scientific and business applications require access to large amounts of data and fast computational resources that may be available in distributed wide area networks. These resources are administrated locally and independently. This creates the need for computational grids, which manage this large collection of heterogeneous and dynamic resources in a scalable way. This paper reviews the unique security requirements of computational grid environments and shows the need for an intrusion detection system in grid environments. Moreover, differences between intrusion detection systems in grid environments and conventional distributed systems are illustrated. This paper introduces a proposed intrusion detection model for computational grid environments and presents how it can be used as part of one of the most leading grid research projects “the Globus Toolkit”.