Yahoo says it has recently identified that hackers accessed its network and stole passwords for over one billion users in August 2013.
This intrusion is separate from the incident reported by Yahoo last September where 500 million user accounts were compromised.
For 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. Yahoo says payment card data and bank account information were not stored in the system the company believes was affected.
Yahoo previously disclosed that its 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, the company believes an unauthorized third party accessed its 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. Yahoo is notifying the affected account holders, and have 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.
Yahoo has not released which country hacked into its systems but Russia, China and North Korea are among the leading culprits.