Yahoo tripled its estimate for the number of accounts affected by an August 2013 data breach to a full 3 billion accounts, the entirety of those registered across Yahoo Mail and other Yahoo-owned properties at the time, the company said Tuesday.
Yahoo, now owned by Verizon (VZN), initially disclosed the compromise of information related to more than 1 billion user accounts on Dec. 14. The hacking was then regarded as the biggest known corporate data breach in history in terms of the number of people affected—a title it usurped from an earlier breach of 500 million Yahoo accounts reported by the company just three months earlier on Sept. 22.
Turns out the biggest known breach was much more massive than previously thought. Hackers potentially gained access to billions more names, email addresses, telephone numbers, birthdates, and hashed passwords than first reported, although Yahoo said it believes that no financial data, such as credit card numbers or bank account details, were stolen.
Yahoo, since merged with the media property AOL under the name “Oath,” said that the company had “recently obtained new intelligence and now believes, following an investigation with the assistance of outside experts, that all Yahoo user accounts were affected” in the four-year-old breach.
The company said it was cooperating with a law enforcement investigation and that it would notify the additional set of affected users via email.
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“Verizon is committed to the highest standards of accountability and transparency, and we proactively work to ensure the safety and security of our users and networks in an evolving landscape of online threats,” said Chandra McMahon, Verizon’s chief information security officer, in a statement. “Our investment in Yahoo is allowing that team to continue to take significant steps to enhance their security, as well as benefit from Verizon’s experience and resources.”
Verizon slashed $350 million off its Yahoo acquisition deal price after learning of the breaches last year.
Equifax, one of the big three credit bureaus, recently disclosed a data breach that potentially affects 145.5 million people. The company revised its estimate for the number of people who had their personal details, such as Social Security numbers, compromised by an additional 2.5 million on Monday.
People who wish to take action or learn more about how the Yahoo hack affects them can read this FAQ on the company’s website.