On Monday, the companies admitted the problem was much bigger.
In prepared remarks, Facebook said inflammatory posts by Russian agents intending to sow discord among Americans reached 126 million users. Google, whose information security director, Richard Salgado, will testify on Tuesday, said that the same agents, from the Kremlin-linked Internet Research Agency, uploaded over 1,000 videos on GoogleÃ¢Â€Â™s YouTube service. Twitter said they published more 131,000 messages on Twitter.
And they admitted they were wading into new territory.
Ã¢Â€ÂœThe abuse of our platform by sophisticated foreign actors to attempt state-sponsored manipulation of elections is a new challenge for us Ã¢Â€Â” and one that we are determined to meet,Ã¢Â€Â TwitterÃ¢Â€Â™s acting general counsel, Sean Edgett, said in written testimony.
FacebookÃ¢Â€Â™s general counsel, Colin Stretch, said in written testimony: Ã¢Â€ÂœThe foreign interference we saw is reprehensible and outrageous and opened a new battleground for our company, our industry, and our society.Ã¢Â€Â
The companies stressed that over all, content connected to the Russian company was a sliver of all they publish daily.
But the new information will only raise more questions: How long did they know of the activity? How far back have they investigated the activity of these accounts? Beyond the Internet Research Agency, were there similar efforts by other foreign-linked companies?
Lawmakers want more tech regulations
The political winds have shifted for Silicon Valley, with a growing number of legislators sounding alarms in recent months over the power that Facebook, Google and Twitter have over public opinion.
Some lawmakers are now proposing to rein them in by regulating political ads on their digital platforms. After Facebook disclosed in September that it had identified more than $100,000 in advertisements paid for by the Internet Research Agency, lawmakers proposed legislation that would websites to submit to the same sort of disclosures rules imposed on broadcast television.
During TuesdayÃ¢Â€Â™s hearing, Senator Amy Klobuchar, Democrat of Minnesota, is expected to make a strong push for a bill that requires sites like Facebook and YouTube to disclose the sources of funding for political ads. She recently introduced the legislation with Senator John McCain, a Republican from Arizona, and Mr. Warner.
Ahead of the hearing, Facebook and Twitter announced they would voluntarily disclose the sources of funding behind political ads. Twitter went further to ban ads from two Kremlin-backed news outlets as well as vowing to disclose the source of funding for all ads.
But lawmakers say self-regulations wonÃ¢Â€Â™t cut it.
Ã¢Â€ÂœIf their policies comply with our bill, they should support our bill and maybe can use their policy as a standard when we pass our bill,Ã¢Â€Â Ms. Klobuchar said in a recent interview.
ItÃ¢Â€Â™s not just about ads
Political ads are just part of the problem. Russian agents also spread nonpaid content through the creation of pages on Facebook dedicated to hot-button issues like race. On Twitter, the Kremlin-connected Internet Research Agency used automatic messaging tools known as bots that could quickly spread tweets through multiple accounts.
Lawmakers will press the companies on what theyÃ¢Â€Â™ve done to to fight misinformation on Ã¢Â€Âœorganic postsÃ¢Â€Â and bots.
TwitterÃ¢Â€Â™s recent announcement to disclose ad funding sources wasnÃ¢Â€Â™t enough, said Adam Schiff of California, the top Democrat on the House Intelligence Committee.
Ã¢Â€ÂœTransparency in advertising alone, however, is not a solution to the deployment of bots that amplify fake or misleading content or to the successful efforts of online trolls to promote divisive messages,Ã¢Â€Â Mr. Schiff said recently.
Another problem is issues-oriented ads that are not defined as political ads because they do not directly promote a political candidate. Such ads would include an environmental group publishing an ad attacking environmental deregulation or anti-immigration groups calling for stricter border policies.
Ã¢Â€ÂœI have a particular concern about issue advertisements, sock puppets, and the dissemination of made-up stories, tactics we know Russia and other actors have used extensively,Ã¢Â€Â Senator Ron Wyden, Democrat of Oregon, said in a statement ahead of a Senate Intelligence Committee hearing on Wednesday with the same executives from Facebook, Google and Twitter. The House Intelligence Committee also has a hearing scheduled.