The Facebook founder told senators the company's delay in identifying Russian efforts to interfere in the 2016 election is "one of [his] biggest regrets in running the company." Zuckerberg said methods to spread political misinformation will keep evolving.
But he added he is hopeful the company is now better prepared to combat election meddling, not only during the 2018 U.S. midterms but also in elections in countries such as India and Brazil.
"This is an arms race. They're going to keep on getting better at this. And we need to invest in keeping on getting better at this too," Zuckerberg said.
"I have more confidence that we're going to get this right," he added.
However, he said he "can't guarantee" that Facebook would stop misinformation entirely. Zuckerberg said it would not be a "realistic expectation."
In his prepared congressional testimony, Zuckerberg said content from one Russian agency that tries to spread misinformation reached about 126 million people on Facebook during a two-year period around the 2016 election. An additional 20 million people may have seen content from the Internet Research Agency on Instagram, a platform Facebook owns, he said.
Zuckerberg said Facebook did not identify election meddling until right around the time of the November 2016 vote. But he expressed confidence in Facebook's ability to identify problems earlier.
The revelation that the personal data of up to 87 million people may have been misused by consulting firm Cambridge Analytica has sparked backlash and dominated much of the hearing. Asked if that pool of people overlapped with the 126 million people who saw content from the Russian agency, he said Facebook is "investigating that" and thinks it "is entirely possible that there will be a connection."