When your Yahoo email is hacked and the hacker does not change the password, the first thing to do is to change the password yourself. If the hacker has changed the password, immediately request a password reset using the Password Helper and contact Yahoo Customer Service to report the incident.
Change Your Password
To change your password, log in to your Yahoo email account, click the gear icon and click the Account Info option. From this page, go to the Account Security tab, where you have the option to change your password. If the hackers changed any of your account information, change it back.
Look for Signs of a Hacked Account
If you suspect your account has been compromised and there are no issues with sending and receiving mail, then check that your personal information is not changed.
Lastly, make sure there is nothing suspicious on your recent activity page.
Add Extra Security
On the Account Security page is an option to enable Two-step verification, which helps secure your account by requiring authentication when you access your account from an unknown device. To activate the two-step verification, you will provide your phone number and Yahoo will send you a validation code.
To decrease the chances of having your account hacked in the future, change your password often, and always use a strong password. When choosing a strong password, make sure it is different for every site. Do not use repeating or sequencing characters. Never choose an obvious or personal set of characters. A strong password will generally have at least eight characters with uppercase and lowercase letters, as well as numbers and symbols.
Report Suspicious Activity
Always report suspicious activity to Yahoo Help. Click the My Account button on the Yahoo Help page. Under the Contact Us drop-down button, click Start here and follow the on-screen guide.
Avoid Future Hacks
Use preventative measures while on the Internet to avoid a hacked account. Always use antivirus software and keep it updated. Do not share personal information over the Internet. Be aware of email scams and do not click on any links in the messages. Immediately report scam emails as spam. Always sign out of your accounts, especially on public or shared computers. Choose a strong password, change it often, and keep your Yahoo account updated.