Facebook's general counsel, Colin Stretch, explained in his opening statement that as many as 126 million Facebook users may have seen content "that originated from the Russian operation."
Facebook had said before that 10 million users may have been exposed to ads purchased by Russian operatives. But the company had not previously discussed how many people saw Russia-linked interference content shared organically through the site.
Much of that content was aimed at widening divides in American culture, touching on topics from LGBT matters to race issues to immigration to gun rights.
"Many of these ads and posts are inflammatory, some are downright offensive, and much of it will be particularly painful to communities that engaged with this content believing it to be authentic," Stretch said. "They have every right to expect more from us."
Stretch and his colleagues are set to face more questions on Capitol Hill Wednesday in an all-day marathon. First they go before the Senate Intelligence Committee in the morning and then before the House Intelligence Committee in the afternoon.
Twitter also revealed that the breadth of Russian propaganda machine was greater than previously reported. Sean Edgett, Twitter's deputy general counsel, said in his opening statement that the company had uncovered 2,752 Russia-linked accounts and more than 36,000 automated "bots." Those accounts tweeted 1.4 million times about the election last fall.
"This type of activity just creates not only a bad user experience, but a distrust for the platform," Edgett said. "So we are committed to working every single day to solving this problem."
For Sen. Amy Klobuchar, D-Minn., that commitment isn't enough. She's pushing legislation that would regulate political ads on the social media sites, similar to how ads are regulated on television and radio.
She pressed the witnesses on whether they would offer support for her bill. They declined to offer their unequivocal backing, but Google's top security security officer, Richard Salgado said they wanted to achieve the same ends.
"We certainly support the goals of the legislation and would like to work through the nuances to make it work for all of us."
Overall, the hearing offered few fireworks.
At one point, Sen. John Kennedy, R-La., expressed his frustration with Facebook for suggesting that it could track the source of funding for all 5 million of its monthly advertisers.
"I think you do enormous good, but your power scares me," he said.
Sen. Al Franken, D-Minn., grew annoyed when Facebook's Stretch wouldn't commit to not accepting money for political ads in other currencies other than the American dollar.
Franken rose his voice as he complained about not being able to understand why it took the social media companies --which market themselves as the keeper of millions of bits of data --so long to see that the Russian government was using them to influence the American election.