Ensure you are no longer using any password that may have been in that 2012 file. Transition to a reputable password manager to generate unique, complex passwords for every site.

If you are researching this file for personal security or academic reasons, here are the steps generally recommended to mitigate risks from such leaks:

Activate Multi-Factor Authentication (MFA) on your Yahoo account and all other critical services.

A group known as D33Ds Company claimed responsibility for the breach.