Facebook is being investigated to assess whether an experiment in which it manipulated users' news feeds to study the effect it had on moods might have broken data protection laws, it has been reported.

The Information Commissioner's Office (ICO) is said to be looking into the experiment carried out by the social network and two US universities in which almost 700,000 users had their news feeds secretly altered to study the impact of ''emotional contagion''.

A spokesman from the ICO said it was too early to tell what part of the law Facebook might have infringed , the Financial Times reported.

The paper added that the Data Protection Commissioner in Ireland will also be contacted as the technology giant's European headquarters are in Dublin.

The experiment was carried out in one week during January 2012 in collaboration with Cornell University and the University of California .

The aim of the government-sponsored study was to see whether positive or negative words in messages would lead to positive or negative content in status updates.

Many users reacted angrily following online reports of the findings, which were published in the June 17 edition of the prestigious Proceedings of the National Academy of Sciences.

Some referred to it as ''creepy'', ''evil'', ''terrifying'' and ''super disturbing''.