A former member of Facebook's Data Science Team has revealed shocking facts about how the social network used data in experiments that made unwitting guinea pigs of its users.

Andrew Ledvina, a former data scientist who worked at Facebook from February 2012 to July 2013, said the social media giant had manipulated the content of news feeds of 689,000 users to see if it would make the account owners sadder or happier.

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"There's no review process, per se. Anyone on that team could run a test. They're always trying to alter people's behavior," Ledvina told the Wall Street Journal.

The eye-opening revelation has stunned millions of Facebook users who thought that the data they accessed and paid attention to was indeed "their" data.

Ledvina also said Facebook ran tests so often that some scientists became worried they might be analyzing the accounts of same people many times.

Facebook assembled a panel of experts in 2012 that consisted of 50 members into a Data Science Team. Team members specialized in areas such as privacy, security and data. Since then, team members have run several tests that seem to go against standard product testing.

"We are taking a very hard look at this process to make more improvements," said a Facebook spokesperson.

Even the COO of Facebook, Sheryl Sandberg, said "Facebook cannot control emotions of users. Facebook will not control emotions of users."

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