With its ever-growing penetration of remote regions of the world, the Internet provides great opportunity for conducting research. Beyond clear advantages such as increased cost-effectiveness and efficiency in collecting large samples, Internet-based research has proven particularly useful in reaching hidden or marginalized populations who engage in illegal or deviant behaviors. However, this new medium for research raises important and complex legal, ethical, and methodological/technological issues that researchers must address, particularly when studying undetected criminal behaviors. The current paper chronicles various issues that were encountered in the implementation of an active Internet-based pilot research study of child pornography (CP) users. Moreover, this study was undertaken to address a critical gap in the existing research on CP offending, which has to date primarily focused on incarcerated or convicted samples. The Internet provides the optimal medium for studying community populations of CP users, given that it has become the primary market for CP distribution. This paper is designed to serve as a guide for researchers interested in conducting Internet-based research studies on criminal and sexually deviant populations, particularly CP offenders. Several recommendations are offered based on our own experiences in the implementation of this study. Copyright © 2009 John Wiley & Sons, Ltd.