You need to keep all the information related to the account safe and secure. Here are the major security concerns you need to take:
1. Use Account Key instead of password to log in to your account.
2. If you are using a password, then turn on the two-step verification.
3. Change your password frequently and make it stronger each time.
4. Use the app specific password for any third party app
5. Always update your recovery option to the latest.
6. Keep a close look of the account sign-in activity
7. Don’t forget to sign out from a public computer
read more: http://www.emailtechnicalcontact.com/yahoo-customer-service.html
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