SybilInfer is an algorithm for labelling nodes in a social network as honest users or Sybils controlled by an adversary. At the heart of SybilInfer lies a probabilistic model of honest social networks, and an inference engine that returns potential regions of dishonest nodes. The Bayesian inference approach to Sybil detection comes with the advantage label has an assigned probability, indicating its degree of certainty. We prove through analytical results as well as experiments on simulated and real-world network topologies that, given standard constraints on the adversary, SybilInfer is secure, in that it successfully distinguishes between honest and dishonest nodes and is not susceptible to manipulation by the adversary. Furthermore, our results show that SybilInfer outperforms state of the art algorithms, both in being more widely applicable, as well as providing vastly more accurate results. 1

Abstract not found

E-commerce strategists advise companies to create virtual communities for their customers. But what does this involve? Research on face-to-face communities identifies the concept of “sense of community: ” a characteristic of successful communities distinguished by members ’ helping behaviors and members’ emotional attachment to the community and other members. Does a sense of virtual community exist in online settings, and what does it consist of? Answering these questions is key, if we are to provide guidance to businesses attempting to create virtual communities. The paper explores the concept of sense of virtual community in a newsgroup we call Multiple Sports Newsgroup (MSN). We first demonstrate that MSN does indeed have a sense of virtual community, but that the dimensions of the sense of community in MSN differ somewhat from those reported for physical communities. The nature of these differences is plausibly related to the differences between electronic and face-to-face communication. We next describe the behavioral processes that contribute to the sense of virtual community at MSN—exchanging support, creating identities and making identifications, and the production of trust. Again, these processes are similar to those found in non-virtual communities, but they are related to the challenges of electronic communication. Lastly, we consider the question of how sense of community may come about and discuss the implications for electronic business.

E-commerce strategists advise companies to create virtual communities for their customers. But what is involved in establishing and maintaining virtual communities? This paper addresses two questions: Does a sense of community similar to that sometimes observed in physical communities also occur in virtual settings? And how is a sense of virtual community maintained? These questions are examined in an intensive study of an established virtual community called MSN. MSN members experienced a sense of community, but the dimensions of sense of community differed somewhat from those reported for physical communities in ways plausibly related to the differences between electronic and face-toface communication. The experienced sense of community in MSN was actively maintained through the social processes of exchanging support, creating identities and making identifications, and the production of trust. Again, these processes are similar to those in non-virtual communities, but related to the challenges of electronic communication. The findings suggest a process model of sense of virtual community creation and maintenance that is simpler and more powerful than previous theories.

Please do not quote from this version, which differs in small ways from the version that appears in print. 7000 words. 1

Although the potential impacts of virtual communities have been widely recognized in business and academia, little research has been done to provide guidelines for design of such communities and to improve the understanding of critical events and interaction patterns that arise during their evolution. This paper reports the results of two years of participative longitudinal study that led to the creation of a leading web site that has attracted more than 300,000 visitors since its inception. The patterns of interaction which led to growth and stabilization of the site are described, the impact of design choices are discussed, and typical events which occur during the gradual formation of community are analyzed. The site is dedicated to football at one of the major academic institutions in the United States. It consists of several interactive fora as well as over 50 pages pertaining to different aspects of the football program. The community was studied through initiation, adoption, and successive design changes. Issues and conflicts that arise in the course of life of a virtual community are traced. Among others, the study found that interactive fora entail a trade-off between “participation ” and “signal-to-noise ” ratio. Based on this study, implications for communities of practice found in organizational settings are developed.

programmer named Jarkko Oikarinen created software for live, typed conversation among