This chapter focuses on the issue of malicious agents in open multi-agent systems (MAS) with discussions in relation to the existing crime study, i.e. supply-demand analysis and deterrence theory. Our work highlights the importance of mechanisms to make intervention into the MAS, in an attempt to deter malicious agents from maximizing their utilities through the illegal actions. Indeed, in market-oriented MAS, human interventions sometimes would be necessary, given the condition that these interventions would not destroy the ecological stability of the agent society. However, an automatic intervention mechanism seems to be the winning card in the end, among them, the reputation mechanism, agent coalition formation etc. It is our hope that our work can shed light on these issues as well as their deployment in MAS.