BOSTON (CBS) – It’s a shocking admission.

Facebook has been secretly manipulating users’ news feeds to measure how their moods change when exposed to good and bad news. Now, the company is facing backlash for subjecting users to a psychological experiment.

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“It does creep me out, I don’t want people wondering what kind of mood I’m in during the day. It’s a personal thing,” said a woman who spoke to WBZ-TV.

When users sign up for Facebook, they agree to allow research studies to be conducted on their profiles. In 2012, Facebook manipulated users’ news feeds without their consent to see whether their moods changed when exposed to positive or negative news.

“I think it is cause for concern,” said Northeastern University Professor Dan Kennedy, a longtime critic of Facebook’s privacy issues.

Kennedy said the move goes beyond standard data-mining for advertising purposes.

“This idea of treating their customers essentially like lab rats to see what the response would be, that strikes me as going beyond what we normally see in marketing studies of any type,” Kennedy said.

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In response to the revelation, Facebook says it has tightened its research practices and is sorry for causing “anxiety.”

Changing the public’s mood about the project, however, may be a challenge.

“What other experiments are going on right now? Maybe in our settings we could have a check box to say if we want to participate in these experiments or not? That would be nice,” said Senior Editor Bridget Carey.

Other people WBZ-TV spoke felt violated by the study.

“They look at your cookies. They see what you’ve searched for on Google. I feel like it can be a violation of privacy,” said a man who spoke to WBZ-TV.

Some Facebook users, however, were unconcerned about the research project. They said that anything they post on social media is available for use. Privacy experts believe they are correct.

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