Facebook is under fire for sneaky research on the social media site – a secret experiment the company now regrets. For a week in January 2012, it conducted a study on 689,000 randomly picked members without their knowledge. Upbeat, emotionally positive posts by friends were removed from some users’ news feeds, while posts expressing sadness, disappointment, anger or other negative words were shielded from another group.

Test subjects' behavior matched their altered timelines. Those who saw more positive posts posted more positive updates of their own, and vice versa. The study disproved "the common worry that seeing friends post positive content leads to people feeling negative or left out," one of the researchers says in a Facebook post last week. "At the same time, we were concerned that exposure to friends' negativity might lead people to avoid visiting Facebook."

The belatedly revealed project sparked a global outcry. A British government body is looking into the experiment to see if members’ data was used without consent. A top Facebook executive, chief operating officer Sheryl Sandberg, tried to soothe anger. "This was part of ongoing research companies do to test different products," she said last week. "It was poorly communicated. And for that communication we apologize. We never meant to upset you."

Critic says: "If you are exposing people to something that causes changes in psychological status, that's experimentation. This is the kind of thing that would require informed consent." -- James Grimmelmann, University of Maryland technology and law professor

Researcher says: "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." – Adam Kramer, Facebook data scientist, in June 29 post

Tech writer says: "Facebook shouldn’t be singled out as a villain. All researchers, whether at universities or technology companies, need to focus more on the ethics of how we learn to improve our work." -- Jaron Lanier, author of "Who Owns the Future" and a Microsoft Research specialist