Facebook released the results of a study where its data scientists skewed the positive or negative emotional content that appeared in the news feeds of nearly 700,000 users over the course of a week in order to study their reaction.

The study was almost certainly legal, a line in the terms of service users agree to when they sign up cedes control of data for “data analysis, testing, [and] research”. But the reaction from many users and commentators has been pretty negative.