Breach is thought to be separate from the 2014 breach.
Yahoo has disclosed the details of another data breach dating in 2013.
The latest revelations to come out of the company show that more than one billion user accounts may have been affected.
Yahoo’s disclosure comes separately from the 2014 breach where the company revealed 500 million accounts had been accessed.
According to the company, which is in the process of being acquired by Verizon, names, phone numbers, passwords and email addresses were all stolen. Bank and payment data has not been stolen.
The company said that it is working with the police and authorities and said in a statement that it: “believes an unauthorised third party, in August 2013, stole data associated with more than one billion user accounts,” and that the breach is: “is likely distinct from the incident the company disclosed on September 22, 2016.”
The latest hack was uncovered during the ongoing investigation by authorities and security experts into the 2014 breach.
Users have been urged to change their passwords and security questions.
Little is currently known about the latest hacking revelations to come out of the company other than that it is being considered a separate event to the 2014 breach, which Yahoo said had been: “stolen by what we believe is a state-sponsored actor.”
Yahoo has been in the news regularly this year after disappointing growth, a massive data breach and its proposed $4.8bn acquisition by Verizon.
The latest hack could put the acquisition in further doubt after Verizon had already said that the 2014 breach could impact the deal.
This references specific legal language in the deal that says Verizon can withdraw if an event occurs which “reasonably can be expected to have a material adverse effect on the business, assets, properties, results of operation or financial condition of the business.”
The results of the Yahoo investigation would likely determine how big the impact was, according to Silliman.
Reuters reports that Yahoo said: “We are confident in Yahoo’s value and we continue to work towards integration with Verizon.”
Now that the investigation has revealed another, even bigger data breach, questions will again be raised about the security of the deal.