As many as 1-billion Yahoo users could have been exposed in a three-year old security breach that the company disclosed yesterday.
Bob Lord, chief information security officer of Yahoo, yesterday issued a statement confirming that the company has conducted an investigation that identified data security issues that might have affected 1-billion user accounts.
The new breach probably happened in August 2013, and is different to the one the company disclosed in September, which affected 500-million user accounts.
“We’ve taken steps to secure those user accounts and we’re working closely with law enforcement,” Lord says.
The company discovered the new heist after law enforcement provided it with data files that a third party claimed was Yahoo user data. “We analyzed this data with the assistance of outside forensic experts and found that it appears to be Yahoo user data,” Lord states.
“Based on further analysis of this data by the forensic experts, we believe an unauthorised third party, in August 2013, stole data associated with more than 1-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 22 September 2016.”
Lord warns that the on potentially-affected accounts, the stolen user account information may 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,” he says. “Payment card data and bank account information are not stored in the system the company believes was affected.”
Yahoo has previously warned users that outside forensic experts are investigating the creation of forged cookies that could allow an intruder to access users’ accounts without a password.
“Based on the ongoing investigation, we believe an unauthorised third party accessed our 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 22 September 2016.”
Yahoo is notifying potentially affected users and has 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 unauthorised access to user accounts.”
Lord urges users to visit Yahoo’s Safety Centre page for recommendations on how to stay secure online.