Some of the philosophy experiments on my website include hidden elements that in effect mean the users are the subjects in experiments they don't know are happening. If I were attached to a university, could I be done for an ethics violation?
In psychology, I think there was concern about Milgram, Zimbardo, Little Albert, Ainsworth's Strange Situation, that kind of thing. Those studies are on the edge even if ultimately one thinks the contribution to human knowledge justifies them.