This is a formal commentary, responding to Matthew Curran Benigni, Kenneth Joseph, and Kathleen Carley's contribution, "Online extremism and the communities that sustain it: Detecting the ISIS supporting community on Twitter". This brief review reflects on the ethics of big data research methodologies, and how novel methods complicate long-standing principles of research ethics. Specifically, the concept of the "data subject" as a corollary, or replacement, of "human subject" is considered.