Facebook has apologised for carrying out secret mood experiments on its users. The social network and two US institutes - Cornell University and the University of California at San Francisco - were involved in the study.were involved in a study to establish the effects of being exposed to positive and negative status updates in 2012.

Breaching the line: The manipulative antics have evoked alot of fury among Facebook users across the world. Pic/Thinkstock

The research involved filling Facebook members’ News Feeds with a collection of either positive or negative updates from their friends to determine whether this affects the tone of their own posts. Users selected for the experiment were not informed of their participation, but Facebook insists the trials were permitted under its terms and conditions.