The FTC opened the investigation in response to news that political data firm Cambridge Analytica obtained personal information from nearly 50 million Facebook users without their consent.
"The FTC is firmly and fully committed to using all of its tools to protect the privacy of consumers," FTC director Tom Pahl said in a statement. "Foremost among these tools is enforcement action against companies that fail to honor privacy promises."
California Attorney General Xavier Becerra, part of a coalition of 37 attorneys general, also sent a letter Monday asking Facebook CEO Mark Zuckerberg to explain how the company was involved in Cambridge Analytica's "manipulation of users' data."
"Facebook left millions of Californians' personal information vulnerable," Becerra said in a statement. "My fellow Attorneys General and I demand answers in behalf of all those whose trust and personal data has been compromised."
Last week, Facebook was hit with four lawsuits in federal court in San Francisco and San Jose.
Facebook, which has more than two billion users worldwide, had no immediate comment on the lawsuits.
But in a statement posted in its online newsroom on Wednesday, the company said, "Protecting people's information is the most important thing we do at Facebook.
"What happened with Cambridge Analytica was a breach of Facebook's trust. More importantly, it was a breach of the trust people place in Facebook to protect their data when they share it," the company said.
Facebook said it is "taking action on potential past abuse and putting stronger protections in place to prevent future abuse.
—Bay City News Service
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