This article analyzes recent cases of company-sponsored online experiments with unsuspecting users and discusses the ethical aspects of such experimentation. These cases illustrate a new type of online research where companies modify their algorithms to intentionally misinform or mislead users. Unlike typical forms of A/B testing, where two versions of the same website are presented to different users to evaluate interface changes, algorithm modification is a deeper form of testing where changes in program code induce user deception. Thus, we propose to call this new approach C/D experimentation to distinguish it from the surface-level website evaluation associated with A/B testing. Three aspects raise ethical concerns regarding C/D experimentation: the absence of user consent to participate in research, the presence of intentional deception, and the complete lack of protection for human subjects who partake in privately funded behavioral research. Three recommendations are proposed to address these issues: (i) to develop an ethical code of conduct for subject protection shared by online companies, (ii) to include special provisions for C/D experiments in social networking platforms, and (iii) to create an independent user advocacy board to protect the rights of users who partake in online research conducted in the private sector.