Yahoo is asking its users to change their passwords, review all their accounts for suspicious activity after identifying a new system breach where hackers are believed to have stolen data from more than one billion user accounts in August 2013, making it the largest breach in history.
As we previously disclosed in November, law enforcement provided Yahoo with data files that a third party claimed was Yahoo user data. The company analyzed the data with the assistance of outside forensic experts and found that it was Yahoo user data.
Based on further analysis of this data by the forensic experts, it is said an unauthorized third party, in August 2013, stole data associated with more than one billion user accounts. “We have not been able to identify the intrusion associated with this theft. We believe this incident is likely distinct from the incident we disclosed on September 22, 2016.” Stated Yahoo.
For potentially affected accounts, the stolen user account information is said to have included names, email addresses, telephone numbers, dates of birth, hashed passwords (using MD5) and, in some cases, encrypted or unencrypted security questions and answers.
The investigation indicates that the stolen information did not include passwords in clear text, payment card data, or bank account information. Payment card data and bank account information are not stored in the system the company believes was affected.
Separately, Yahoo previously disclosed that our outside forensic experts were investigating the creation of forged cookies that could allow an intruder to access users’ accounts without a password. Based on the ongoing investigation, it has been confirmed that an unauthorized third party accessed the company’s proprietary code to learn how to forge cookies.
The outside forensic experts have identified user accounts for which they believe forged cookies were taken or used. “We are notifying the affected account holders, and have invalidated the forged cookies. We have connected some of this activity to the same state-sponsored actor believed to be responsible for the data theft the company disclosed on September 22, 2016.”
“We are notifying potentially affected users and have taken steps to secure their accounts, including requiring users to change their passwords. We have also invalidated unencrypted security questions and answers so that they cannot be used to access an account. With respect to the cookie forging activity, we invalidated the forged cookies and hardened our systems to secure them against similar attacks. We continuously enhance our safeguards and systems that detect and prevent unauthorized access to user accounts.” Stated Yahoo