Facebook briefed members of both the Senate and House of Representatives intelligence committees on Wednesday about the suspected Russian advertising, according to a congressional source familiar with the matter.
Facebook didn't publicly release the thousands of online messages it says it now believes were paid for by Russians, but the company has said that the "vast majority" of ads involved "didn't specifically reference the USA presidential election, voting or a particular candidate". "But there's a lot more questions".
The fake accounts were discovered during a company review of ad sales that was spurred by a broader investigation the company initiated into Russian meddling after the election, Mr Stamos said. This ad spending was connected to about 470 "inauthentic accounts and [Facebook] Pages in violation of our policies", Stamos said. Still, Facebook has struggled with exactly how transparent to be about its processes and how deeply to police its users.
The company said about 3,000 ads were bought by people operating almost 500 fake Facebook accounts.
Editor's Remarks: Facebook has been criticised for not cracking down on the dissemination of misinformation on its site and has now started to release data that they say, "amplified divisive and political messages across the ideological spectrum" during the USA election campaign.
Furthermore, "sophisticated voter targeting" would presumably bombard voters in key swing states or precincts with fake news ads, but 75 percent of the roughly 3,000 questionable Russian ads Facebook found were national in scope.
"The idea that fake news, of which it's a very small amount of the content, influenced the election in any way is a pretty insane idea", Facebook CEO Mark Zuckerberg said in the immediate aftermath of the election. "We originally reported on attempts to misuse our platform in April, and as our internal review continued, we found additional activity that we published yesterday". In a statement posted days after the election, Facebook founder Mark Zuckerberg promised to explore the issue but said that 99 percent of information found on Facebook is authentic and only "a very small amount" is fake or hoaxes. "Given the revelations of the past few days regarding the secret purchase of thousands of internet political ads by foreign actors during the 2016 presidential election, there can no longer reasonably be any doubt that we need to revise and modernize our internet disclaimer regulations".
Of those targeted ads, the company said, more ran in 2015 than 2016.
A spokesman for Mueller's office declined to comment on whether it has sought or will seek subpoenas from the grand jury it is working with to obtain Facebook's records.
Facebook also allows advertisers to create "unpublished page posts", sometimes referred to by researchers in the field as "dark posts".
"You can, from anywhere in the world, advertise to the entire world through the platform", said Nathan Persily, a Stanford University law professor.
"I think we may just be seeing the tip of the iceberg", the Virginia Democrat told reporters in response to Facebook's Wednesday disclosure that apparent Russian-tied accounts spent some $150,000 on more than 5,200 political ads previous year. The companies may rush now to self-regulate to stave off government action, he said.
US intelligence agencies also say Russian operatives unleashed automated attacks using computer commands known as "bots" to circulate fake news about Clinton, often via phony Twitter accounts.
Hillary Clinton and her supporters managed to lose the United States presidential election despite pumping $1.2 billion into their effort.
The social media giant is under new scrutiny after an about-face.
Warner wasn't suggesting a legislative solution would go through the Intelligence Committee, according to Rachel Cohen, a spokeswoman for the senator.
Watchdog group Common Cause on Thursday filed a complaint with the U.S. Justice Department and the Federal Election Commission alleging that unknown foreign nationals made expenditures during the election in violation of American election law.
Clint Watts, a former Federal Bureau of Investigation agent who has studied Russian online influence campaigns, said Wednesday that Facebook's report served as "validation" for findings by him and his researchers, who he said had spotted what they believed to be Russians posing as Americans to press political messages on Facebook as early as 2015.
How was the Russian company able to buy the ads?