Facebook has said it recently discovered a security breach affecting nearly 50 million user accounts.
The company said hackers exploited the View As feature on the service.
Facebook says it has taken steps to fix the security problem and alerted law enforcement.
Sky News reported the social media giant is investigating whether the accounts were misused or information was accessed.
More than two billion users use Facebook every month, and another two million use messaging service WhatsApp and photo sharing app Instagram – which are both owned by Facebook.
The New York Times said the company discovered the breach earlier this week after discovering that hackers had exploited a feature in Facebook’s code which allowed them to access user accounts.