Why did I receive an Account Key text from Yahoo?

We'll send an Account Key text when you create a Yahoo account or make security changes to an existing account. You'll need to enter the Account Key when prompted to confirm your account or changes. 

If you received an Account Key text but didn't create an account or make security changes, then someone else mistyped their number and accidentally used yours. Don't worry, they won't be able to move forward with your mobile number because they don't have possession of your phone to get the Account Key.