Yahoo has admitted to another hack that could mean as many as one billion users' accounts have been compromised.
The breach, which has quickly earned the title of the largest in history, took place in August 2013 and was uncovered by Yahoo as it was investigating the 2014 hack, which it has since said was "state sponsored" and saw 500 million accounts put at risk.
Yahoo says "this incident is likely distinct from the incident we disclosed on September 22, 2016," and said that while it's been working with law enforcement and a third-party cybersecurity firm to trace its origin, it doesn't yet know who the perpetrator was.
"As we previously disclosed in November, law enforcement provided us with data files that a third party claimed was Yahoo user data," Yahoo's chief information security officer Bob Lord said in a statement.
"We analysed this data with the assistance of outside forensic experts and found that it appears to be Yahoo user data. Based on further analysis of this data by the forensic experts, we believe an unauthorized third party, in August 2013, stole data associated with more than one billion user accounts."
Stolen user account information may have included names, email addresses, phone numbers, dates of birth, "hashed" passwords and, in some cases, encrypted or unencrypted security questions and answers.
In addition, Lord said the attackers had worked out a way to forge "cookies" that Yahoo places on user computers when they log in that contain a great deal of information about the user, such as whether that the user has already authenticated to the company's servers.
Payment card data and bank account information were not stored in the system believed to be affected and the hackers did not obtain passwords in clear text, the company said.
Among the one billion victims are more than 150,000 US government and military employees, according to a Bloomberg report, which claims that these accounts belong to current and former White House staff, congressmen and their aides, FBI agents, officials at the National Security Agency, the Central Intelligence Agency, the Office of the Director of National Intelligence, and each branch of the US military.
Yahoo says it is notifying the account holders affected in the breach and that users will be required to change their passwords. However, we'd advise completely deleting your Yahoo account instead.
"As we've said all along, we will evaluate the situation as Yahoo continues its investigation," a Verizon spokesperson said. "We will review the impact of this new development before reaching any final conclusions."
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