In January 2012, Facebook secretly manipulated the news feeds of 689,003 users for one week, reducing exposure to either positive or negative emotional content to study 'emotional contagion.' The results, published in PNAS in June 2014, showed Facebook could make users sadder or happier by controlling what they saw. No informed consent was obtained. The study included children and adolescents without parental consent. Facebook's only justification was that users had agreed to general terms of service. Lead author later apologized for 'the way the paper described the research.'