Facebook is facing new calls for regulation and has been hit with questions about personal data safeguards after reports that a political consultant gained inappropriate access to the data of 50 millions users.

The social media giant disclosed the issue in a blog post on Friday, hours before media reports that conservative-leaning Cambridge Analytica, a data company known for its work on Donald Trump's 2016 presidential campaign, was given access to the data, starting in 2014, and may not have deleted it.

The scrutiny presented a new threat to Facebook's reputation, which was already under attack over Russians' alleged use of Facebook tools to sway American voters before and after the 2016 US elections.

Facebook said the root of the problem was that researchers and Cambridge Analytica lied to it and abused its policies, but critics threw blame at Facebook as well and called for new regulations.

Facebook insisted the data was misused but not stolen, because users gave permission, sparking a debate about what constitutes a hack that must be disclosed to customers.

"The lid is being opened on the black box of Facebook's data practices, and the picture is not pretty," said Frank Pasquale, a University of Maryland law professor.

He said Facebook's response that data had not technically been stolen seemed to obfuscate the central issue that data was apparently used in a way contrary to the expectations of users. "It amazes me that they are trying to make this about nomenclature. I guess that's all they have left," he said.

Democratic US Senator Mark Warner said the episode bolstered the need for new regulations about internet advertising, describing the industry as the "Wild West".

"Whether it's allowing Russians to purchase political ads, or extensive micro-targeting based on ill-gotten user data, it's clear that, left unregulated, this market will continue to be prone to deception and lacking in transparency," he said.

'The New York Times' and 'The Observer' reported that private information from more than 50 million Facebook users improperly ended up in the hands of Cambridge Analytica, and the information has not been deleted despite Facebook's demands beginning in 2015.

Some 270,000 people allowed use of their data by a researcher, who scraped the data of all their friends as well, a move allowed by Facebook until 2015.

The researcher sold the data to Cambridge, which was against Facebook rules, the newspapers said.

Cambridge Analytica worked on Trump's 2016 campaign. However, a Trump campaign official said it used Republican data sources.

Facebook said its policies had been broken by Cambridge Analytica and researchers and that it was exploring legal action.

Cambridge Analytica in turn said it had deleted all the data and that the company supplying it had been responsible for obtaining it.

Andrew Bosworth, a Facebook vice president, hinted the company could make more changes to demonstrate it values privacy. "We must do better and will," he wrote on Twitter.

Irish Independent