in part because the large number of questioners gave little time for followup. he began by formally apologizing for the host of issues plaguing facebook. >> it's clear now that we didn't do enough to prevent these tools from being used for harm, as well. that goes for fake news, for foreign interference in elections, and hate speech, as well as developers and data privacy. >> last month it was revealed that a firm with ties to president trump's campaign accessed the data of 87 million users without their consent. that angered users, advertisers, lawmakers already struggling with facebook's role in spreading misinformation and allowing election meddling. while zuckerberg said he was open to regulation, he deflected questions about specifics saying this -- >> yes, and i'll have my team follow up with you so that way we can have this discussion across the different categories where i think that this discussion needs to happen. >> look forward to it. >> wall street liked that answer. and wall street liked zuckerberg's testimony. facebook shares rose 4.5%