Yahoo Inc. has uncovered yet another massive cyber attack, with data from more than one billion user accounts compromised in August 2013, making it the largest breach in history.
The number of affected accounts was double the scope of an attack in 2014 that the internet company disclosed in September, Reuters reports.
News of that attack, which affected at least 500 million accounts, prompted Verizon Communication Inc. to say in October that it might withdraw from an agreement to buy Yahoo’s core internet business for US$4.83 billion.
Yahoo said the incident disclosed on Wednesday was likely distinct from the one it reported in September.
The company said it has not been able to identify the intrusion associated with the theft.
Yahoo said the stolen user account information may have included names, e-mail addresses, telephone numbers, dates of birth, hashed passwords and, in some cases, encrypted or unencrypted security questions and answers.
Payment card data and bank account information were not stored in the system believed to be affected, the company said.
Yahoo said it is notifying potentially affected users and has taken steps to secure their accounts.
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