Yahoo has disclosed that a new security breach has affected more than one billion email accounts. The breach dates back to 2013 and is thought to be separate from a massive cyber security incident that impacted nearly 500 million — announced in September.
Yahoo believes an unauthorised third party stole user data from more than one billion accounts in August 2013. That data may have included names, e-mail addresses and passwords, but not financial information.
The company will notify users who may be affected and has begun requiring users to change their passwords.
The security incident, likely one of the largest cybersecurity breaches ever, comes less than three months after Yahoo admitted data from at least 500 million accounts had been stolen.
Earlier breach, which Yahoo has attributed to a state-sponsored actor, is likely distinct from the newly disclosed breach.
Yahoo has taken steps to secure user accounts and is working closely with law enforcement.
For affected email accounts, the stolen user account information may have included names, email addresses, telephone numbers, date 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.
Yahoo is notifying affected users and has taken steps to secure their accounts, including requiring users to change their passwords. Yahoo has also invalidated unencrypted security questions and answers so that they cannot be used to access an account.
Separately, Yahoo previously disclosed that its forensic experts were investigating the creation of forged cookies that could allow an intruder to access users’ accounts without a password. Based on the investigation, the company believes an unauthorized third party accessed Yahoo’s proprietary code to learn how to forge cookies.
The forensic experts have identified user accounts for which they believe forged cookies were taken or used. Yahoo is notifying the affected account holders, and has invalidated the forged cookies. The company has 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.