April 10 (UPI) -- In testimony Tuesday on Capitol Hill, Facebook CEO Mark Zuckerberg told lawmakers he's "committed to getting this right" after millions of the site's users possibly fell victim to a data breach.
Lawmakers summoned Zuckerberg for more than five hours to ask him about the Cambridge Analytica data breach that resulted in possibly 87 million people unwittingly disclosing their personal information.
Zuckerberg defended his company's response to the data breach, but said its actions didn't go far enough.
"We took down the app, and we demanded that both the app developer and Cambridge Analytica delete and stop using any data that they had," he said. "They told us that they did this. In retrospect, it was clearly a mistake to believe them."
In the future, Zuckerberg pledged to "conduct a full audit" of Facebook apps the company determines to be suspicious.
"If we find that they're doing anything improper, we'll ban them from Facebook and we will tell everyone affected," he said.
Facebook has taken steps to make it easier for users to control what they share and delete collected data. Monday, the site began allowing users to see if their information was shared.
Sen. Joe Kennedy, R-La., added a suggestion for further improvement, telling Zuckerberg that Facebook's current user agreement "sucks."
"The purpose of that user agreement is to cover Facebook's rear-end," Kennedy said. "It's not to inform your users about their rights. Now, you know that and I know that. I am going to suggest to you that you go back home and you rewrite it."
Zuckerberg also said Facebook employees were cooperating with special counsel Robert Mueller's probe into Russian meddling in the 2016 election. He confirmed Mueller's team has interviewed Facebook employees while speaking to members of the Senate's judiciary and commerce committees.
"I want to clarify, I'm not sure we have subpoenas," Zuckerberg said. "I know we're working with them."
He added that one of his "greatest regrets" is his company's slow response to pinpoint Russian bad actors on Facebook during that election cycle.
By the end of the trading day on the New York Stock Exchange, Facebook stock was up about 4.5 percent.
On Wednesday, Zuckerberg will testify before the House Energy and Commerce Committee at 10 a.m.