(Adds comments by Zuckerberg, members of Congress, committee chairman)
WASHINGTON/SAN FRANCISCO, April 11 (Reuters) - Facebook Inc Chief Executive Mark Zuckerberg on Wednesday sparred with lawmakers over how much control users of the world's largest social media network have over their data in a sometimes fractious five-hour hearing.
Zuckerberg assured members of the U.S. House of Representatives Energy and Commerce Committee that users have ultimate control of their Facebook information, but undermined that by saying he was among the 87 million users whose data was improperly shared with political consultancy Cambridge Analytica.
His admission that even the company's tech-savvy founder was unable to protect his own information underscored the problem Facebook has in persuading skeptical lawmakers that users can easily safeguard their own information and that further legislation governing Facebook is unnecessary.
"Every time that someone chooses to share something on Facebook ... there is a control. Right there. Not buried in the settings somewhere but right there," the 33-year-old internet billionaire told the hearing.
Yet, when asked if his data had been improperly shared with Cambridge Analytica, he replied: "Yes." He gave no further details.
The Cambridge Analytica issue was the reason Zuckerberg was on Capitol Hill, answering questions for the second time in two days about how the group - which has counted U.S. President Donald Trump's election campaign among its clients - got hold of data on many millions of Facebook users.
"How can consumers have control over their data when Facebook does not have control over the data?" asked Representative Frank Pallone of New Jersey, the ranking Democrat on the Energy and Commerce committee, at the beginning of the hearing.
Democratic Representative Debbie Dingell said Facebook used computer code embedded in websites to gather dossiers on virtually everyone online, whether they like it or not.
"It doesnt matter whether you have a Facebook account. Through those tools, Facebook is able to collect information from all of us," she said, referring to Facebook "Like" buttons that appear on many websites. Zuckerberg was unable to answer Dingell when she asked how many website pages had such buttons.
Dingell expressed frustration with Zuckerberg's frequent promises to get back to lawmakers later in writing. "Some things are striking during this conversation," she said. "As CEO, you didnt know some key facts."
The issues of data privacy and control dominated the session, which was more focused and antagonistic than a Senate hearing the day before.
Wearing a dark suit and tie and prefacing almost every remark with "Congressman" or "Congresswoman," Zuckerberg appeared even more controlled than he did on Tuesday, as he refrained from cracking jokes and flashed few smiles.
Zuckerberg repeatedly defended the company's practices, saying that users have control over their own data and decide what to share.
He said he was not familiar with so-called "shadow profiles," which media reports have described as collections of data about users that they have no knowledge of or control over. He also said Facebook does not collect information from users' verbal conversations through mobile devices' microphones.
However, in a series of questions on how people can remove data from Facebook, Zuckerberg said that Facebook does "collect data on people who are not signed up for Facebook for security purposes." He had no response when asked how a person who is not a Facebook member can remove information without first signing up for the service.
Regarding the Cambridge Analytica issue, Zuckerberg said it will take "many months" to complete an audit of other apps that may also have improperly gathered or shared data.
"I do imagine that we will find some apps that were either doing something suspicious or misusing people's data," he said.
As he did on Tuesday, Zuckerberg made no further promises to support new legislation or change how the social network does business.
Facebook shares closed up 1.2 percent on Wednesday after dips earlier in the day. They posted their biggest daily gain in nearly two years on Tuesday as Zuckerberg managed to deter any specific discussion about new regulations that might hamper Facebook's ability to sell ads tailored to users' profiles.
"It is inevitable that there will need to be some regulation" of internet firms, Zuckerberg said on Wednesday, but he again steered away from any specifics.
The House committee Chairman Greg Walden told reporters he would discuss with his committee holding similar hearings with other technology chief executives. He did not name specific companies.
"This is a wake-up call to Silicon Valley and the tech community that if you let these things get out of hand, having grown up in a very lightly regulated environment, you could end up with a lot more regulation than you seek, he said after the hearing.
(Reporting by Dustin Volz and David Shepardson in Washington and David Ingram in San Francisco; editing by Bill Rigby and Susan Thomas)