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.