(NBC News) Facebook CEO Mark Zuckerberg returned to Capitol Hill Wednesday for a second day of testimony on his company's failure to protect user data and Russian meddling in the 2016 elections.
On Tuesday Zuckerberg disclosed his company is working with special counsel Robert Mueller's investigation of Russia election meddling after a pro-Trump data mining firm accessed at least 87-million users information without their knowledge.
In his testimony before the House, Zuckerberg also warned there's no guarantee similar efforts can be stopped in the future.
"For as long as Russia has people employed who are trying to perpetrate this kind of interference, it will be a hard for us to guarantee that we're going to fully stop everything," he said.
Facebook is now increasing its internal security, offering money to people who report data breaches and labeling all political and issue ads with exactly who paid for them.
Still, lawmakers say if Facebook and other social media sites can't better protect followers personal information, then Congress will pass privacy regulations.
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