Via Hearthstone®: http://ift.tt/2sAgBhp
Here at Blizzard we take account security seriously, which is why we recommend all accounts have an authenticator attached. Two-Factor Authentication such as this makes it much harder for someone to access your account as login required not only your password but a physical item such as a phone or a token. Having an authenticator has been proven to drastically increase account security; on top of that it can also make using online self-service account recovery a much smoother process.
While security is a serious issue we wanted to offer our community the most user friendly experience. This is why we introduced the One-Button Authenticator last year to our Blizzard Authenticator app:
Whenever* a log in attempt occurs on your account you will be notified via the app and prompted to Approve or Deny the request. You can also approve log in requests with notifications on your mobile or smartwatch without even opening the app! You can find out more about authenticators on our Battle.net Authenticator FAQ.
*Please note that by default you will only need to approve a log in attempt once a week per device. You can change this setting on your Battle.net Account Management page.