According to the statement, an attack on one of Quora’s systems has compromised user account details, including their full names, email addresses and passwords, data imported from linked networks such as Facebook and Twitter, as well as non-public user activity like direct messages, downvotes, and answer requests. However, the “overwhelming majority” of content accessed was already public, the company said. Yet questions and answers written anonymously had not been affected due to the company not storing identities of these users.

Quora said it had discovered the attack on Friday, and had since launched an investigation with its internal security teams and a digital forensics and security firm. The company has notified law enforcement officials.

“We recently discovered that some user data was compromised as a result of unauthorised access to one of our systems by a malicious third party,” said CEO Adam D’Angelo in a statement. “We are working rapidly to investigate the situation further and take the appropriate steps to prevent such incidents in the future.”

“We believe we’ve identified the root cause and taken steps to address the issue, although our investigation is ongoing, and we’ll continue to make security improvements,” he added.

D’Angelo said the company was working to notify and log out any users who may have been affected, “out of an abundance of caution”. Returning users will need to set new passwords, as old passwords have now been invalidated.

“It is our responsibility to make sure things like this don’t happen, and we failed to meet that responsibility. We recognise that in order to maintain user trust, we need to work very hard to make sure this does not happen again,” D’Angelo wrote. “There’s little hope of sharing and growing the world’s knowledge if those doing so cannot feel safe and secure, and cannot trust that their information will remain private.”

Quora, which was founded in 2009 by two Facebook alumni, allows users to submit, answer and edit questions. This year, Quora reported attracting up to 300 million monthly users.

The attack on Quora follows a series of high-profile hacks affecting billions of people, including a breach of Marriott’s guest reservation system last week, exposing data belonging to 500 million people and reportedly following a string of smaller security breaches.

According to the statement, an attack on one of Quora’s systems has compromised user account details, including their full names, email addresses and passwords, data imported from linked networks such as Facebook and Twitter, as well as non-public user activity like direct messages, downvotes, and answer requests. However, the “overwhelming majority” of content accessed was already public, the company said. Yet questions and answers written anonymously had not been affected due to the company not storing identities of these users.

Quora said it had discovered the attack on Friday, and had since launched an investigation with its internal security teams and a digital forensics and security firm. The company has notified law enforcement officials.

“We recently discovered that some user data was compromised as a result of unauthorised access to one of our systems by a malicious third party,” said CEO Adam D’Angelo in a statement. “We are working rapidly to investigate the situation further and take the appropriate steps to prevent such incidents in the future.”

“We believe we’ve identified the root cause and taken steps to address the issue, although our investigation is ongoing, and we’ll continue to make security improvements,” he added.

D’Angelo said the company was working to notify and log out any users who may have been affected, “out of an abundance of caution”. Returning users will need to set new passwords, as old passwords have now been invalidated.

“It is our responsibility to make sure things like this don’t happen, and we failed to meet that responsibility. We recognise that in order to maintain user trust, we need to work very hard to make sure this does not happen again,” D’Angelo wrote. “There’s little hope of sharing and growing the world’s knowledge if those doing so cannot feel safe and secure, and cannot trust that their information will remain private.”

Quora, which was founded in 2009 by two Facebook alumni, allows users to submit, answer and edit questions. This year, Quora reported attracting up to 300 million monthly users.

The attack on Quora follows a series of high-profile hacks affecting billions of people, including a breach of Marriott’s guest reservation system last week, exposing data belonging to 500 million people and reportedly following a string of smaller security breaches.