Major tech companies are delivering testimony for the first time in public on Capitol Hill as part of congressional investigators ongoing probe into Russian interference in the 2016 election.
Representatives from Facebook, Twitter and Google testified before the Senate Judiciary Committee about what they know about specific attempts by Russian trolls to disseminate disinformation, political ads purchased on their given sites and what efforts they are taking now to prevent further incidents of meddling from happening in future elections.
The companies are also set to testify on Wednesday before the House and Senate Intelligence Committees, as well.
Follow Senate testimony updates below:
Second panel concludes
The second panel concluded at 5:32 p.m.
Graham concluded the hearing by expressing his condolences to those whose lives were affected by the apparent terrorist attack in New York City.
Kennedy: First Amendment implications "concern" me
Sen. John Kennedy said he is also concerned about the First Amendment implications of removing or censoring content just because someone finds it offensive.
What, he asked, is fake news?
The witnesses said they think they can find agreeable parameters.
Expert says there's been an "explosion in chatter" related to New York incident
Smith, the terrorism analyst, said there has been an "explosion in chatter" during the hearing, related to the New York incident authorities are investigating as a terrorist attack.
At least six are dead in what authorities are considering a deliberate attack in lower Manhattan. Police and witnesses have told CBS News a motorist drove onto a busy bicycle path near the World Trade Center memorial and struck several people, then emerged from the vehicle screaming and brandishing imitation firearms.
"America's war with itself has already begun," expert says
Clint Watts, the fellow at the Foreign Policy Research Institute, emphasized the seriousness of bad actors bending the use of social media to their wills.
"America's war with itself has already begun," he said.
Watts has previously testified before the Senate on similar topics.
First panel concludes, second begins
The first panel concludes, with the second panel convening immediately.
The experts testifying in the second panel are Clint Watts, a fellow at the Foreign Policy Research Institute, and Michael S. Smith II, a terrorism analyst based in South Carolina.
Kennedy corners witnesses on how much they know about users
Sen. John Kennedy asked just how much Facebook knows about individual users, and whether it could compile a database of say, all teenagers who are depressed.
Facebook's lawyer said they have configured their systems so the company can't target individuals, or compile demographic groups, like that.
Franken: “How could you not connect those two dots?”
Sen. Al Franken asked how Facebook didn't realize the purchase of political ads with rubles -- Russia's denomination -- were suspect.
"How could you not connect those two dots?" Franken said.
Stretch said that, in hindsight, they should have taken a broader approach to vetting those ads.
But Stretch would not agree to Franken's request that he commit to not allowing foreign currency to purchase political ads. Stretch did say he could commit to not allowing foreign actors to purchase U.S. political ads.
Cruz: Silicon Valley censoring speech is "troubling"
Sen. Ted Cruz said it should be "troubling" to anyone who values democracy that companies in Silicon Valley are censoring speech.
Cruz said that during the 2016 election, stories from conservative outlets and about conservative candidates were being underrepresented or excluded entirely. He also noted a more recent incident, when Rep. Marsha Blackburn was temporarily censored on Twitter for language she used.
Cruz said it's "disconcerting" if political opinions are censored.
Facebook's top lawyer said his company sees Facebook as a platform for ideas, and doesn't discriminate. But he would not say the platform was "neutral," as its algorithm tailor content to an individual's tastes.
Coons criticizes companies' "slow, halting steps" to combat Russian influence
Sen. Chris Coons called the continued developments related to Russian influence surrounding the 2016 election "truly troubling."
Coons criticized the companies' "slow, halting steps" to stop and to prevent Russian influence. Coons questioned how Facebook didn't detect "fraud" events sooner.
Flake asks how Twitter, Facebook detect threats
Sen. Jeff Flake, who recently announced he will not run for re-election, asked the social media company representatives how they detect threats.
For Facebook and Twitter, an algorithm detects anything that could be a threat, and that algorithm kicks it to a human reviewer as necessary, the witnesses testified.
Kennedy to witnesses: Your power sometimes "scares me"
Sen. John Kennedy said he is "proud" the companies represented are American companies.
But he said the vast power of the companies represented at the Senate panel Tuesday "scares me."
He pinned Facebook's top lawyer to answer questions as to which countries interfered in the election, and asked how he can know with certainty which foreign actors are manipulating advertising.
Feinstein asks why YouTube gave RT preferred status
Feinstein asked why RT -- formerly known as Russia Today -- was given a "preferred" status by YouTube.
Richard Salgado, the director for law enforcement and information security at Google, said that was dropped because of declining viewership, but Feinstein asked why it received that status in the first place, and kept it so long.
After election, fake accounts questioned legitimacy of Trump's election: Witnesses
The witnesses suggested that up until the election, these fake accounts tied to foreign actors like Russia tried to create discord through hot-button issues.
After the election, the witnesses agreed, they saw accounts questioning the legitimacy of Mr. Trump's election.
Twitter's top lawyer: We have heard the concerns
Sean Edgett, the acting general counsel for Twitter, said Twitter has heard the concerns from the public after reports of Russian election meddling.
"Twitter is familiar with problems of spam and automation, including how they can be used to amplify messages," he said in his written testimony. "Twitter also has experience fighting online extremist content. ... Today, we intend to demonstrate the seriousness of our commitment to addressing this new threat, both through the effort that we are devoting to uncovering what happened in 2016 and by taking steps to prevent it from happening again."
Edgett said Twitter's first priority was to make sure nothing like that was repeated in future elections.
His full written testimony is available here.
Facebook's counsel: Foreign interference is "reprehensible"
Facebook's general counsel, Colin Stretch, said foreign interference in the 2016 election goes against Facebook's values, calling it "reprehensible."
Stretch said Facebook takes what happened during the 2016 election very seriously. The company's own investigation is ongoing, he said, describing the changes the company is making.
Stretch's full written testimony is available here.
Feinstein: It's shocking how easy Russian manipulation was
Sen. Feinstein said that, for the first time, she finally understands the extent of Russian's "frightening" power to use social media.
Feinstein said it shouldn't shock anyone that Russia worked to influence the election. But what is shocking is how simple it was, she said. Feinstein described how she says Russian trolls used hot-button issues like gun rights to influence public opinion.
"This is really a critical hearing," Feinstein said.
Trump's social media comes up
In his opening statement, Graham read a comment President Trump previously made to Fox News.
Mr. Trump said he didn't think he would be where he is without social media. Graham said social media to the president, himself and other politicians is "invaluable."
But challenges remain, he said.
"I think this is the national security challenge of the 21st Century."
Graham calls hearing to order
Graham, chairman of the subcommittee, called the hearing to order at 2:31 p.m.
(See his statement on the hearing in an earlier post.)
Hearing about to begin, witnesses arrive
The hearing, set for 2:30 p.m., is about to begin.
The witnesses took their seats, as journalists gathered around with cameras.
Here's what Mark Warner wants to know
The Senate Intelligence Committee will have its own hearing on social media manipulation on Wednesday.
Sen. Mark Warner, D-Virginia, the vice chairman of that committee, tweeted what he wants to know from companies like Twitter and Facebook.
Social media company shareholders request more accountability
Shareholders in Facebook, Google and Twitter have filed proposals in the last week demanding more accountability related to any foreign meddling in the 2016 election.
The shareholders are also interested in what they see as a growth of hate speech and disinformation on the platforms. One proposal filed by Arjuna Capital to Alphabet, the parent company of Google, Twitter, and Facebook calls on the companies to issue reports on "major global content management controversies," and another proposal filed by the Park Foundation to Facebook asks the social media giant consider establishing a Risk oversight Committee.
"Like Congress and the American public, shareholders in these companies have serious questions and concerns about how these platforms were used and abused during the 2016 election," Michael Connor, Executive Director of Open MIC, a nonprofit organization that works with shareholders of social media and technology companies, said in a statement. "The investors, through these filings, intend to play a critically important role in holding Facebook, Google and Twitter accountable for what happens on their platforms."
Facebook deleted 5.8 million accounts before 2016 election
Facebook shut down 5.8 million fake accounts in the U.S. in the weeks before the 2016 election, according to a source familiar with the testimony Facebook will deliver to the committee.
The social media company removed the accounts in October. But Facebook is expected to acknowledge its automated tooling didn't reflect the current understand that numerous fake accounts were being used to advance political causes, the source told CBS News.
Graham: Manipulation of social media "one of the greatest challenges to American democracy"
Sen. Lindsey Graham, R-South Carolina, had strong words ahead of the hearing on Russia disinformation on the web.
Graham, chairman of the Senate Judiciary Committee's subcommittee on crime and terrorism, said the manipulation of social media "is one of the greatest challenges to American democracy," as well as to national security.
"The purpose of today's hearing is to gather information regarding activity by foreign governments and terrorist organizations to manipulate popular social media sites in order to undermine our national security," Graham said in a statement.
"It is well documented that radical Islamic terrorist groups regularly use popular social media outlets to recruit Americans and individuals throughout the world to their cause. It has become equally clear that foreign governments like Russia - in the 2016 election cycle - were deeply involved in manipulating popular social media websites with misinformation to sow discord among Americans. Today's hearing is designed to explore the depth of the problem to determine whether or not legislative solutions are necessary and can be constructed consistent with our Constitution and values. Equally important is to make sure that the social media platforms are doing everything possible to combat these growing concerns. Clearly, to date, their efforts have been unsuccessful."
"The manipulation of social media sites by terrorist organizations and foreign governments is one of the greatest challenges to American democracy and a significant threat to our national security in the 21st century."
Feinstein says it’s time for social media companies to “step up”
Sen. Dianne Feinstein, a California Democrat who sits on the Senate Intelligence and Senate Judiciary committees, said it's time for social media companies like Facebook and Twitter to pay heed to the problem of foreign influence.
"It really is time for them to step up and recognize that we have a problem," she told reporters Tuesday, saying, "these companies are going to have to adjust what they do to meet the national security concerns of this nation. You clearly cannot have the internet use to interfere with an election or to sort of use fake news on their own to convince people of a point of view."
Feinstein said an outside consultant briefed her last week to help her see "how big and widespread" this ability to manipulate on social media is.