The paper addresses several ethical issues in online communication research in light of digital ontology as well as the epistemological questions raised by the blurring boundary between fact and theory in this field. The concept of ontology is used in a Heideggerian sense as related to the human capacity of world construction on the basis of the givenness of our being-in-the-world. Ethical dilemmas of Internet research thus arise from the tension between bodily existence and the proper object of research, i.e., online existence. The following issues are being considered: online identity, online language, online consent and confidentiality. We also argue that research ethics in the US follows the utilitarian tradition, while European researchers are deontologically oriented. A guideline of best practice in online research ethics is proposed.