Popular question-and-answer website Quora said it believes it has identified the root cause of the hacking of as many as 100 million user accounts as the company quickly dealt with the effects of a major hacking breach.

We’re very sorry for any concern or inconvenience this may cause,” said Quora CEO Adam D’Angelo.

Quora sent out emails to its users warning them of the hacking, apologizing and assuring them that the company was investigating the matter.

“We’re in the process of notifying users whose data has been compromised,” Quora told its users in an email. “Out of an abundance of caution, we are logging out all Quora users who may have been affected, and, if they use a password as their authentication method, we are invalidating their passwords.”

Quora is a social media question-and-answer website where questions are asked, answered, edited, and organized by its community of users in the form of opinions. It was founded in 2009 and has its headquarters in Mountain View, California.

Among the data that may have been compromised are account names, email addresses, encrypted passwords, data imported from linked networks when authorized by users, public content and actions (questions, answers, comments and upvotes).

Non-public content and actions – answer requests, downvotes, direct messages are also included in the breach.

Meanwhile, account users have been advised to change their passwords and directed to a help center. D’Angelo said they would issue periodic updates on developments in the probe. 

He added: “It is our responsibility to make sure things like this don’t happen, and we failed to meet that responsibility.”