WASHINGTON • Internet giants Facebook, Google and Twitter told Congress they are not sure they have measured the full extent of Russia's manipulation of social networks in last year's US presidential campaign and they do not yet have the technology to prevent it from happening again.
But the companies vowed to redouble their efforts - literally in the case of Facebook, whose general counsel said the company will double its safety and security staff to 20,000, including contract workers, by the end of 2018 to help track foreign meddling and extremist postings on its sites.
"We need to understand the behaviour and we need to have the capacity both as a company and as an industry to be able to track it and eradicate it," Facebook's chief lawyer, Mr Colin Stretch, said at a Senate Judiciary subcommittee hearing.
US senators on Tuesday pressed Facebook on why the company did not catch 2016 election ads bought using Russian roubles, why its investigation of them took so long and how much it knows about its five million advertisers.
Democrats and Republicans at the Senate crime sub-committee hearing fired questions for much of two hours at Mr Stretch, who said that in retrospect the company should have done more.
The hearing marked the first time tech executives have appeared publicly before US lawmakers on the Russia matter, and the tone represented a dramatic shift in fortunes for Silicon Valley, which for years has grown accustomed to favourable regulatory treatment in the US.
Lawyers for Twitter and Alphabet's Google also faced questions at the hearing about how Russians used their services, but Facebook drew the bulk of senators' ire because of its unique role in targeted marketing on the Internet. Facebook has broader reach than the smaller Twitter network, and it offers more powerful targeting capabilities than Google.
"Why has it taken Facebook 11 months to come forward and help us understand the scope of this problem?" Democratic Senator Chris Coons asked.
Mr Stretch responded that, when US spy agencies alleged in January that Russians meddled in last year's election, "we weren't sitting around". The company over the following months launched an investigation and reported the results, he said.
Republican Senator Lindsey Graham, chairman of the crime subcommittee, also pressed Mr Stretch on whether Iran and North Korea could try to do what Russia did. The lawyer responded: "Certainly potentially. The Internet is borderless."
Hanging over Facebook, Google and Twitter is the threat of legislation that would extend rules governing political advertising on television, radio and satellite to also cover social media. Lawyers for the three companies were scheduled to return to Capitol Hill yesterday for two more hearings on Russia ad spending.