Facebook is dealing with a lot of unhappy users Monday morning after the Menlo Park company tweaked the feeds of thousands of users, the Today Show reported.
Researchers changed the feeds of almost 700,000 users to show a disproportionate number of happy or sad statuses for one week in 2012.
They found the emotions of others on users' news feeds can affect their moods, but they did not inform users of the experiment. And now, many of them are calling it unethical--but it is not illegal.
When users sign up for the social network, they agree to give up their data for testing and research.
The findings were published in the Proceedings of the National Academy of Sciences in an article called, "Experimental evidence of massive-scale emotional contagion through social networks."
An author of the study, Adam Kramer, has apologized on his personal Facebook page:
"I can understand why some people have concerns about it, and my coauthors 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."