Facebook's Sheryl Sandberg is testifying alongside Twitter's Jack Dorsey.
Executives from Facebook Inc and Twitter Inc defended their companies to skeptical US lawmakers on Wednesday over what many members of Congress see as a failure to combat continuing foreign efforts to influence US politics.
At the start of the hearing Senator Mark Warner, the committee’s Democratic vice chairman, said the companies were not doing enough to stop the flow of foreign influence and threatened Congressional action.
Social media stocks fell after his remarks, with Twitter down 5.7 percent and Facebook around 1.8 percent lower.
Shares of Alphabet Inc, the parent of Google, sank 2.7 percent.
Facebook Chief Operating Officer Sheryl Sandberg, who testified alongside Twitter Chief Executive Jack Dorsey, acknowledged that the company was too slow to respond to Russian efforts to interfere in the 2016 US election, but insisted it is doing better.
“We’ve removed hundreds of pages and accounts involved in coordinated inauthentic behavior - meaning they misled others about who they were and what they were doing,” Sandberg told the Senate Intelligence Committee.
“When bad actors try to use our site, we will block them,” she said.
Dorsey, sporting a straggly beard, nose ring and open-collared shirt, insisted Twitter’s monitoring has tightened, including notifying law enforcement last month of accounts that appeared to be located in Iran.
The committee also asked Alphabet Inc’s Google to testify, but declined an offer to send Chief Legal Officer Kent Walker rather than Alphabet Chief Executive Larry Page.
Facebook, Twitter and other technology firms have been on the defensive for many months over political influence activity on their sites as well as concerns over user privacy.
“Unfortunately, what I described as a ‘national security vulnerability,’ and ‘unacceptable risk,’ back in November remains unaddressed,” Senator Richard Burr, the committee’s Republican chairman, said.
“Clearly, this problem is not going away. I’m not even sure it’s trending in the right direction,” he added.
Warner said social media companies were doing better at combating disinformation, but their efforts were insufficient.
“I’m skeptical that, ultimately, you’ll be able to truly address this challenge on your own. Congress is going to have to take action here,” Warner said.
Republican Senator Susan Collins said she had learned from a university report that she had been targeted some 270 times by Russian-linked tolls on Twitter, asking Dorsey why the company does not tell users when they have been attacked.
Dorsey said it was “unacceptable” that she was not told.
Before the hearing, President Donald Trump, without offering evidence, accused the companies themselves of interfering in the upcoming US mid-term elections, telling the Daily Caller that social media firms are “super liberal.”
Trump told the conservative outlet in an interview conducted on Tuesday that “I think they already have” interfered in the Novmeber 6 election.
The report gave no other details.
Executives from the companies, which have repeatedly denied political bias, have traveled to Washington several times to testify in Congress, including 10 hours of questioning of Facebook Chief Executive Mark Zuckerberg over two days in April.
Senate Intelligence has been looking into Russian efforts to influence US public opinion throughout Trump’s presidency, after US intelligence agencies concluded that Kremlin-backed entities sought to boost his chances of winning the White House in 2016.
Moscow denies involvement, and Trump - backed by some of his fellow Republicans in Congress - has repeatedly dismissed investigations of the issue as a partisan witch hunt or hoax.