The possibilities for carrying out online research are growing rapidly, enabling researchers to collect previously unavailable data about online behaviours and interactions. While such techniques provide exciting opportunities for researchers they can present ethical challenges. In this paper we explore these ethical dilemmas with particular reference to the new methods used to explore online virtual environments, the ability to re-use online data from multiple sources and the global reach of the Internet. We conclude by highlighting the key issues that need to be considered by researchers both in terms of developing their own ethical viewpoints as well as the development of future institutional and professional ethical codes of practice for online research.