You'll no longer need to remember complicated passwords when you use Yahoo Account Key to access your account. To sign in, tap "Yes" on the notification we send to your mobile phone. With Account Key enabled, there's no password on your account, so no one other than you can sign in.
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Voila! No more passwords. To sign in from now on, you'll just need to enter your username and click Continue and then we'll send your phone a notification to approve access.
Currently, if I was to lose my phone AND someone could bypass my 4-digit password to get in, they could easily access all my email accounts.
With the Yahoo Account Key, the individual would need to know my username, so this would appear to be an improvement.
Two questions that are not addressed in the Yahoo FAQs:
1) If I wish to log in from my computer rather than my phone, will that also require using my phone to get a key? If the answer is yes but I've lost my phone, wouldn't I be locked out?
2) What about those of us who do not pay to roam our cells when we travel abroad? How would we access our email?