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."
Sen. John Kennedy, R-La., said Zuckerberg has a choice between fixing Facebook's problems himself or seeing Congress pass legislation to do so. That applies not only to what he called Facebook's "propaganda" problem but also its user privacy issues.
"Here's what's going to happen. There are going to be a whole bunch of bills introduced to regulate Facebook," Kennedy said. "It's up to you whether they pass or not. You can go back home, spend $10 million on lobbyists and fight us, or you can go back home and help us solve this problem."
He said the platform's user agreement "sucks" and encouraged Zuckerberg to rewrite it in a way consumers can better understand.
On the elections front, Zuckerberg highlighted efforts to identify misinformation and remove "tens of thousands" of fake accounts sharing content related to elections in France and Germany, as well as a special Senate election in the United States. By later this year, Facebook will have 20,000 people reviewing content, he said.
Facebook also plans to verify advertisers running political and issue ads as soon as later this year, Zuckerberg said. It plans to voluntarily comply with part of the Honest Ads Act, legislation introduced in the Senate that aims to increase transparency in political advertising online.
Asked more than once if he would become a "strong advocate" to make sure that bill passes, Zuckerberg would not commit. He said he thinks it is is more important to "implement it."
Zuckerberg said Facebook plans to require a valid government identification and verify the location of the person behind an ad. However, a hole could exist in that plan.
Asked if a Russian could set up a shell corporation in Delaware without Facebook knowing the person is not actually in Delaware, Zuckerberg responded, "That's correct."