Facebook experiment sparks controversy over the weekend. According to The Guardian, Facebook is facing a "storm of protest" after revealing that it learned how to make users "feel happier or sadder with a few computer key strokes." With this, FB offered an explanation posted by Adam Kramer, one of the co-author of the research, which explains the objective of the study.

"Having written and designed this experiment myself, I can tell you that our goal was never to upset anyone," says Kramer. "I can understand why some people have concerns about it, and my co-authors and I are very sorry for the way the paper described the research and any anxiety it caused. In hindsight, the research benefits of the paper may not have justified all of this anxiety." Kramer says that Facebook has improved its internal review practices since 2012, and future research will take the reaction to this study into account.

Reportedly, the social media network has published details of this experiment in which it manipulated information posted on 689,000 users' home pages and found it could make people feel more positive or negative through a process of "emotional contagion".

"The reason we did this research is because we care about the emotional impact of Facebook and the people that use our product," says Kramer. "We felt that it was important to investigate the common worry that seeing friends post positive content leads to people feeling negative or left out. At the same time, we were concerned that exposure to friends' negativity might lead people to avoid visiting Facebook."

"Emotions expressed by friends, via online social networks, influence our own moods, constituting, to our knowledge, the first experimental evidence for massive-scale emotional contagion via social networks," the study concluded.

Meanwhile, The Guardian reported that lawyers, internet activists and politicians reacted this weekend saying that the mass experiment in emotional manipulation was "scandalous", "spooky" and "disturbing."