Early systems for networked intrusion detection (or, more generally, intrusion or misuse management) required either a centralized architecture or a centralized decision-making point, even when the data gathering was distributed. More recently, researchers have developed far more decentralized intrusion detection systems using a variety of techniques. Such systems often rely upon data sharing between sites which do not have a common administrator and therefore cooperation will be required in order to detect and respond to security incidents. It has therefore become important to address cooperation and data sharing in a formal manner. In this paper, we discuss the detection of distributed attacks across cooperating enterprises. We begin by defining relationships between cooperative hosts, then use the take-grant model to identify both when a host could identify a widespread attack and when that host is at increased risk due to data sharing. We further refine our definition of potential identification using access, integrity, and cooperation policies which limit sharing. Finally, we include a brief description of both a simple Prolog model encorporating data sharing policies and a prototype cooperative intrusion detection system.