Today, Facebook provided additional information on the data breach it disclosed last month. Whereas it initially said up to 50 million users might have been affected, it now reports that 30 million were impacted by the breach. By exploiting a system vulnerability, attackers were able to steal digital keys called access tokens from those 30 million users, and Facebook has now laid out how those users were affected. The company is also notifying those impacted, but if you don't want to wait to be notified, you can check if your account was affected through this link. The 30 million users whose access tokens were stolen fall into one of three categories.