Quora, the popular question-and-answer website, said Monday evening that hackers broke into one of its systems and compromised information from approximately 100 million users.

CEO Adam D'Angelo said in a blog post the company discovered last week that a malicious third party had gained unauthorized access to one of its systems.

Account information, including names, email addresses and encrypted passwords, may have been illegally accessed, according to the post. User-imported data from other social networks could also have been taken.

But the majority of the content the hackers accessed was already public on the site — such as questions, answers, and comments, D'Angelo wrote.

"We're in the process of notifying users whose data has been compromised," he said.