This article deals with the topic of ethics in large‐scale online studies on social network sides. “Big data” and large‐scale online field studies are a relatively new phenomenon and clear ethical guidelines for social science research are still lacking. In this article, I focus on the ethical question of getting informed consent when we collect data from social network sites (SNS). I argue that data from SNS are not per se public and research based on these data should not be exempt from the ethical standard that informed consent must be obtained from participants. Based on the concept of privacy in context (Nissenbaum, ), I further propose that this is because the norms of distribution and appropriateness are violated when researchers manipulate online contexts and collect data without consent. Finally, I make suggestions for existing and possible future practices for large‐scale online studies.