Analysts have warned that Facebook Inc. (FB) could face greater regulatory scrutiny and a subsequent loss of advertising revenue in the wake of controversial allegations that Cambridge Analytica, the data analysis firm that helped President Donald Trump win the U.S. election, obtained private information on tens of millions of the social network's users without their consent.

Facebook blamed the data leak on a rogue professor, who it claimed designed a personality-analysis app for academic purposes and then, without the company’s permission, passed on the data of 50 millions users to Cambridge Analytica.

Sources speaking with The New York Times, which broke this story, said that Cambridge still possessed most if not all the data. The social media network said it is conducting a “comprehensive internal and external review” to verify if this is true.(See also: Zuckerberg Sold $357M in Facebook Stock in Feb.)

Facebook’s shares fell over 3 percent in pre-market trading. The technology-dominated Nasdaq index was also down 1 percent.

Government officials in the U.S. and Europe are now said to be calling for CEO Mark Zuckerberg to appear in front of lawmakers. Regulators believe the company's latest data breach may have violated a landmark consent decree with a federal watchdog agency designed to prevent privacy violations. If found guilty, Facebook could face millions of dollars’ worth of fines and tougher regulation.

Brian Wieser, a senior analyst at Pivotal, warned in a research note, reported on by Bloomberg, that this latest setback makes the stock higher-risk to own. Wieser believes the leak provides another sign of “systemic problems” at Facebook and warned that key advertising customers, over time, could be put off by the increasing likelihood of more stringent regulatory scrutiny.

Wieser doesn’t expect Facebook to be “meaningfully impacted for now,” but warned that advertisers might eventually become frustrated should the breach lead to sweeping changes on how data is collected.

GBH Insights’s Daniel Ives was similarly cautious about the prospect of U.S. and European regulators introducing new measures to restrict how Facebook and its partners collect data. In a research note, reported on by Barron’s, the analyst claimed that extra regulation could negatively impact the company’s advertising business model over the next few years. (See also: France to Sue Apple, Google for 'Abusive Trade Practices'.)

"While it's background noise for investors in the near-term, with the News Feed overhaul and other actions that Facebook has implemented over the past few months, it’s clear with more 'heat in the kitchen from the Beltway' that further modest changes to their business model around advertising and news feeds/content could be in store over the next 12 to 18 months," wrote Ives.

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