Facebook has set up a page to let its users know if they were affected by a recent hack involving information from tens of millions accounts.

The social media behemoth says approximately 30 million of its two billion accounts were affected.

Hackers were able to access information including email address and phone numbers by exploiting bugs in Facebook’s code. About half of affected users also had their birthdays, hometowns and Facebook search history made vulnerable.

Facebook has said it will directly contact people who were affected by the hack. It has also created a webpage where logged-in users can immediately learn if their information was exposed by scrolling down. Users who are not believed to be victims of the hack receive a message saying “Based on what we've learned so far, your Facebook account has not been impacted by this security incident. If we find more Facebook accounts were impacted, we will reset their access tokens and notify those accounts.”

It is not clear who was behind the hack. The FBI is investigating.