The social media giant, which has more than two billion users worldwide, announced last month that engineers had discovered a "security issue" which affected 50 million accounts.
For those that had no idea that this happened, essentially hackers abused a security hole in the "View As" feature on your profile that let you check whether your profile had private information visible to other people, friends, or the general public.
The tokens allowed the hackers to steal name and contact details, which include phone number and/or email, for 15 million people.
He said the FBI has asked the company " not to discuss who may be behind this attack" or to share other details that could compromise its investigation. The data can be used for all sorts of schemes by sophisticated hackers. You will find different set of messages (notifiers) depending on whether or not your account was hacked.
Rosen said this will fall into three groups.
The company said that it may still not know the full extent of the attack and wasn't ruling out the possibility of other "smaller-scale attacks" linked to the breach.
"Once you've become a target, it never ends", he said.
They could then craft a more sophisticated email aimed at tricking users into providing login information on a fake page or into clicking on an attachment that would infect their computers.
As a result impacted users were briefly logged out of their Facebook accounts and needed to sign in again in order to gain access. You'll see one of several detailed notices. In Sri Lanka, Myanmar and other countries, hundreds of people have been killed, partly because of the rampant spread of misinformation across social networks and other internet sites.
By deleting your account, you will remove your personal information from Facebook's servers.
Facebook says third-party apps and Facebook apps like WhatsApp and Instagram were unaffected by the breach. On Monday, Facebook debuted Portal, the company's first hardware device built from the ground up, for high-definition video calls.
Previously, the company said only profile information exposed in the "View As" feature was accessed, which is basically a user's name, gender and hometown.
Facebook fixed the bugs and alerted users on September 28 that the accounts of about 50 million users had been compromised.
Rosen said Facebook has seen no evidence yet that the hackers have been using the stolen data.
The FBI is "actively investigating" the breach, Guy Rosen, a Facebook vice-president, told reporters on a call Friday.
Moreover, Facebook has now confirmed that hackers did actually steal data of over 29 million users.