If you receive a message stating that your account has been locked for security reasons, this means that there have been too many attempts to sign in to your account with the incorrect password. As a security measure, your account has been locked to prevent unauthorized users from being able to access it.

If you haven’t been trying to sign in to your account with the wrong password, this is not necessarily cause for concern. It could simply be the result of another user mistakenly thinking that your ID is theirs.

The lock on your account will expire 12 hours after it was initially locked—the lockout period will not reset each time you attempt to sign in while the account is still locked. You can try to sign in again after the lock has expired

Solution :

First, visit http://login.yahoo.com/config/login
( The first attempt can will fail, say incorrect password or something… Don’t Worry … It’s the second attempt that matters ). You will see this time, a word verification. This is a secure system by which only humans could be making the request, bots cannot see the text, they see encrypted numbers. For some, this is it, the account will log in again! For others, it’s not so. You have to wait up to 12-48hrs for the account to come back.