The highly sophisticated and rapidly evolving area of internet commerce security presents many novel challenges for the organization of discourse in reasoning communities. This chapter suggests appropriate reasoning methods and demonstrates how establishing reasoning communities of security experts and enabling productive group discourse among them can play a crucial role in successful resolution of problems concerning the implementation, integration, deployment and maintenance of flexible local security systems for defense against malware threats in internet security. Local security systems of this sort may combine several ready open source or commercial software packages behind a common front-end and may enhance and supplement their facilities with additional plug-ins. To illustrate the diverse character of challenges the reasoning communities in internet security are likely to be faced with, this chapter concentrates on defense against phishing attacks. This example was selected as it is one of the newest and most rapidly changing application domains for the principles of organizing reasoning communities. The major group discourse methods suggested for the reasoning communities of security experts in this chapter include the Delphi Method, the Wideband Delphi Process, the Generic/Actual Argument Model of Structured Reasoning, Brainstorming, Reverse Brainstorming, Consensus Decision Making, Voting, Open Delphi and Open Brainstorming Methods. The Delphi Method and Wideband Delphi Process are suggested as tools for organizing a cohesive reasoning architecture, for coordinating other methods, and for preparing and allocating other methods to particular issues.