A study carried out by Facebook and two universities has angered users who have accused the social network of manipulating their emotions.
The US technology firm secretly altered the news feeds of 700,000 users as part of the study, which explored “emotional contagion”.
The social network tampered with the algorithm which controls users’ feeds in order to find out how the changes affect their moods.
Researchers wanted to see if positive or negative words in messages led to positive or negative content in users’ status updates.
The study took place over one week in 2012, and was conducted in conjunction with Cornell University and the University of California.
The findings were published in the June 17 edition of the Proceedings of the National Academy of Sciences.
The researchers found that once users had been exposed to positive or negative words in their feeds, their updates changed accordingly.
“Emotional states can be transferred to others via emotional contagion, leading people to experience the same emotions without their awareness,” the study authors wrote.
“These results indicate that emotions expressed by others on Facebook influence our own emotions, constituting experimental evidence for massive-scale contagion via social networks.”
The findings became known more widely on social media after the online magazine Slate and The Atlantic website wrote about it.
Facebook users have taken to Twitter to express their anger at the study.
“#Facebook MANIPULATED USER FEEDS FOR MASSIVE PSYCH EXPERIMENT… Yeah, time to close FB acct!” one Twitter post read.
Other users referred to the study as “super disturbing”, “creepy” and “evil”.
Facebook told The Atlantic that they “carefully consider” their research, and have “a strong internal review process”.