This week, Facebook announced that it has undergone an experiment on mood manipulation involving users' news feed. Privacy activists, including the Electronic Privacy Information Center (EPIC), were not amused with the study.

In the organization's response to Facebook's purported data manipulation, EPIC has filed a formal complaint with the Federal Trade Commission over the 2012 study, the Wire reported. According to EPIC, Facebook have violated privacy laws when it had conducted the experiment without the consent of its users.

"At the time of the experiment, Facebook did not state in the Data Use Policy that user data would be used for research purposes. Facebook also failed to inform users that their personal information would be shared with researchers," EPIC stated in the complaint.

Facebook has since apologized for its controversial secret study, Daily Mail said. During a session organized by the Federation of Indian chambers of Commerce and Industry in New Delhi, Facebook Chief Operating Officer Sheryl Sandberg said in her address in the gathering, "This was part of ongoing research companies do to test different products, and that was what it was; it was poorly communicated. And for that communication we apologize. We never meant to upset you."

Before the apology extended by Sandberg, Facebook have already responded to EPIC's formal complaint with the FTC and said in a separate statement, "When someone signs up for Facebook, we've always asked permission to use their information to provide and enhance the services we offer. To suggest we conducted any corporate research without permission is complete fiction. Companies that want to improve their services use the information their customers provide, whether their privacy policy uses the word 'research' or not."

The Wire said that another digital rights advocacy organization may join EPIC in its complaint. Center for Digital Democracy executive director Jeffrey Chester is reportedly speaking with the regulator next week regarding the controversial study.