DATA watchdogs are ­investigating whether ­Facebook Inc violated data protection laws when it allowed researchers to conduct a psychological experiment on its users.

A Facebook spokesman acknowledged that the experiment on nearly 700,000 unwitting users in 2012 had caused upset and said the firm would change the way it handled research in future.

The study, to find if ­Facebook could alter the emotional state of users and prompt them to post either more positive or negative content, has caused a furore on social media, including on Facebook itself.

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Ireland's Data Protection Commission (DPC) has confirmed it has been in contact with the web giant's Dublin headquarters to ask for a comprehensive explanation of the secret test. The question of user consent is understood to be a major issue for the Irish watchdog.

The UK's Information Commissioner's Office spokesman Greg Jones added: "We're aware of this issue and will be speaking to Facebook, as well as liaising with the Irish data protection authority, to learn more about the circumstances."

Mr Jones said it was too early to tell what part of the law may have been infringed.

Facebook spokesman Matt Steinfeld said: "We are happy to answer any questions regulators may have."