If you use an authenticator – and we hope you do – you may soon notice that an authenticator prompt may not appear with every login. We’ve recently updated our authentication system to intelligently track your login locations, and if you’re logging in consistently from the same place, you may not be asked for an authenticator code. This change is being made to make the authenticator process less intrusive when we’re sure the person logging in to your account is you.
We hope to continue improving the authenticator system to ensure the same or greater security, while improving and adding features to make having one a more user friendly experience. If you don’t already have a Battle.net Authenticator attached to your account, don’t wait until it’s too late - http://us.battle.net/en/security/checklist