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In this paper, we propose an approach that uses in-game reputation as a solution to the problem of cheating in massively multiplayer online games. What constitutes cheating is however quite context-specific and subjective, and there is no universal view. Thus our approach aims to adjust to the particular forms of cheating to which players object rather than deciding a priori which forms of cheating should be controlled.The main feature of our approach is an architecture and model for maintaining player-based and context-appropriate trust and reputation measures, with the integration of these into the game's ranking system. When an avatar loses reputation, our approach intervenes to reduce its ranking. It is envisaged that players will come to attach value to reputation in its own right. We also present the results of relatively large-scale simulations of various scenarios involving sequences of encounters between players, with an initial implementation of our reputation and ranking model in place, to observe the impact on cheaters (and non-cheaters).

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In this paper we discuss the different kinds of contract that are required for the delivery of multi-service networks based on ATM. A growth in the number and complexity of such contracts is predicted and a need is identified for consistent terminology and structured analysis. We establish a framework in this paper for discussing, distinguishing between, and relating different kinds of ATM contracts. The idea of a session contract is introduced to refer to agreements relating to service usage. The impact of the value chain on such contracts is discussed and a categorisation of contract elements is proposed. Some observations are made about the possibilities for automated contract negotiation and implementation.

This paper describes a collaborative approach to handling dynamic attack threats in mobile ad hoc networks. Our approach is biologically and socially motivated. Each network node maintains a trust score for each other node of which it is aware and distributes these to its neighbourhood. Services have associated trust thresholds -the more sensitive the service, the higher the threshold. We define a robust decentralised dynamic system involving nodes, services and trust scores that helps to quickly and reliably locate potential sources of attacks and their threat level. The paper presents results of simulations of the behaviour of the system's dynamics and its interpretation in the context of ad hoc networks.

Abstract-The effectiveness of current anti-spam systems is limited by the ability of spammers to adapt to filtering techniques and the lack of incentive for mail servers to filter outgoing spam. A new approach, based on decentralised trust management, is described in this paper. An architecture and protocol, called TOPAS (Trust Overlay Protocol for Anti Spam), are presented. Each mail server records trust measures relating to each other mail server of which it is aware. Trust by one mail server in another is influenced by direct experience as well as recommendations issued by collaborating mail servers. The TOPAS protocol specifies how these experiences and recommendations are communicated between each spam filter and its associated trust manager, and between trust managers of different mail servers. A technique for improving mail filtering performance and the TOPAS protocol using these trust measures is also described. Finally, experimental work is presented that illustrates use of the protocol in a simulated network scenario. Initial results illustrate the dynamics of this system, and indicate the potential of this approach to significantly improve rates of false positives and false negatives in anti-spam systems. This is an extended version of a paper presented at the Availability, Reliability and Security Conference in April 2007 [1].

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