In recent days, Adobe user database was hacked exposing User Data of many users. In the wake of Adobe hack, Facebook has sent out notifications to some of its customers to change their account passwords.
Facebook has sent the password change request to those customers which are using the same credentials for Adobe and Facebook account.
Although Facebook wasn’t a target of hackers, similar data in Adobe and Facebook logins could risk Facebook User Data as well. Facebook asks customers to answer few questions and set a new password for their Facebook account. Facebook was able to discover the same email-password combos by running them through the same code it uses to confirm your credentials at login time.
Change your password regularly and always keep different passwords for different sites.