Facebook conducted a controversial study on users without their knowledge or permission.
Back in 2012, Facebook adjusted the news feeds of 700-thousand members to try and see if happy posts made them sadder, or the opposite.
The results of the experiment, conducted by researchers from Cornell, the University of California, San Francisco and Facebook, were published this month in the Journal Proceedings of the National Academy of Science.
Many people are angry Facebook didn't ask permission first.
Are you upset Facebook was messing with your emotions?