Like predatory journals, predatory conferences are a growing part of the academic landscape, but unlike their journal counterparts, to date predatory conferences have not been extensively investigated, and many unanswered questions about their workings exist. From a positive ethics perspective, a more complete understanding of predatory conferences is desirable, as it can support researchers in making ethically appropriate choices about conference attendance. Ten predatory conference organisations were the focus of this study. The investigation first set out to identify and document the attributes of such conferences. They were then analysed to understand which attributes can most easily and reliably be used to distinguish them from legitimate conferences. A tool to assist prospective participants is introduced. The implications for positive ethics, in terms of making decisions about conference attendance, are discussed.