Facebook founder Mark Zuckerberg's revealed his own details were among those sold to Cambridge Analytica.
He's faced questions from US politicians for a second day over the data privacy scandal.
Congresswoman Anna Eshoo asked if his own data had been "included in the data sold to the malicious third parties".
Mr Zuckerberg delayed before replying: "Yes."
In statements released ahead of the hearing, he admitted to being "idealistic" and said he did not grasp how the data of the platform's two billion people could be abused.
Up to 87 million users had their information accessed by a Facebook app.
Over 44,000 people in Ireland may also have had their data improperly shared.
Mr Zuckerberg was asked whether the social network plans to take action against the app's creator, Aleksandr Kogan.
"Congressman, it's something that we're looking into.
"We already took action by banning him from the platform, and we're going to be doing a full audit to make sure that he gets rid of all the date that he has as well".
