Avoidance and discovery of security vulnerabilities in information systems requires awareness of typical risks and a good understanding of vulnerabilities and their exploitations. In this paper we compare common methods of sharing security related knowledge with regard to their ability to support avoidance and discovery of vulnerabilities. We suggest a new method of collaborative attack modeling that is especially suitable for this purpose. This method combines a graph-based attack modeling technique with ideas of a Web-based collaboration tool. Keywords security, attack modeling, collaborative knowledge management