A Yahoo security breach revealed in December 2016 was so bad that it made Verizon think twice about buying the internet company, but new reports show that the hack was even worse than initially thought.

The security breach, which happened in August 2013, apparently affected not just over 1 billion users, but all 3 billion Yahoo accounts at the time.

Yahoo Data Breach Affected All Users

Yahoo, which was officially acquired by Verizon for $4.5 billion in June and now under Oath, disclosed in a statement that after acquiring new intelligence, it now believes that all Yahoo user accounts that were activated at the time of August 2013 security breach were compromised by hackers.

Yahoo said that the stolen data does not include clear-text passwords, credit card details, or bank account information. Instead, the compromised data included phone numbers, birth dates, scrambled passwords, and security questions with answers.

Yahoo has started sending email notifications to the additional accounts now believed to have also been affected and continues to work with law enforcement in the investigation of the incident. The company, however, has still not revealed who was behind the August 2013 cyberattack, which Yahoo claimed was a state-sponsored action. It has also not identified the country that backed the hackers.

What Should Yahoo Users Do?

With the August 2013 data breach now known to have affected all Yahoo users at the time, the need to protect personal data has intensified. The things that Yahoo users can do to prevent their compromised information from being used against them have not changed since last year's data breach, but it is probably a good idea to revisit them.

First and foremost, for Yahoo users who have not yet changed their passwords after news of the August 2013 hack broke out last year, you are urged to do so now. In addition, users should also change the password for other online accounts that share the same one as their Yahoo account.

On top of passwords, with the hackers coming away with security questions and answers, it is also recommended to change them for your Yahoo account. Users are also highly recommended to activate two-factor authentication for their Yahoo account and other online profiles that offer the feature.

Lastly and probably most important of all, users should always be mindful of the best practices in keeping their devices safe from potential attacks. Users should never click on suspicious links, and should only download software and content from trusted sources.