Facebook is facing a storm of protest after admitting manipulating users’ emotions in a ‘disturbing’ experiment.

It modified hundreds of thousands of users’ accounts by adding or deleting ‘positive emotional content’ to see if it could make them happier or sadder – without telling them what it was doing.

Researchers from Cornell University and the University of California filtered information going into the ‘news feeds’ – the constant flow of links, videos, pictures, and comments by friends – of 689,000 users.

When ‘positive emotional content’ from friends was reduced, users would post more negative content themselves, essentially becoming unhappier. The opposite happened when ‘negative emotional content’ was reduced.

The process has been dubbed ’emotional contagion’..

The study, published earlier this month in the journal Proceedings of the National Academy of Sciences of the USA, concluded: ‘Emotions expressed by friends, via online social networks, influence our own moods, constituting, to our knowledge, the first experimental evidence for massive-scale emotional contagion via social networks.’

However, people have called for Facebook to be taken to court over what they described as a ‘terrifying’ study.