Yahoo on Wednesday announced another major data breach against the company, the second such announcement in 3 months. The online service says up to 1 billion users had their data accessed by an unauthorized party in August 2013.
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. Payment card data and bank account information are not stored in the system the company believes was affected.
Yahoo is notifying users who may have been affected by the breach, and says it has taken steps to secure their accounts, including requiring the users to change their passwords. Yahoo says the security questions and answers that may have been accessed in the breach have been invalidated, and cannot be used to access a Yahoo account.
The company says the hack was discovered after law enforcement officials supplied the firm with what appeared to be Yahoo user data from an unknown third party. while the company says it hasn’t been able to identify exactly when the breach occurred, it is “likely” different from the late 2014 hack that compromised the data of over 500 million accounts.
In late September, Yahoo admitted that at least 500 million user accounts were compromised by hackers in a late 2014 attack. The hackers were able to grab customer information, including names, email addresses, phone numbers, birthdates, and hashed passwords, as well as both encrypted and unencrypted security questions and answers.
In addition to the above two breaches, the company also disclosed that outside forensics experts were investigating how an intruder created forged cookies, using them to access accounts.
Separately, 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 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. 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.
As is usual in cases like this, the company suggest users review all of their online accounts, to check for suspicious activity, and change any passwords for other accounts that may have shared a password with their Yahoo account. The service also recommends using Yahoo Account Key, a two-factor authentication tool that eliminates the need to use a password on Yahoo altogether.
The text of the email sent to Yahoo users is available below:
NOTICE OF DATA BREACH
We are writing to inform you about a data security issue that may involve your Yahoo account information. We have taken steps to secure your account and are working closely with law enforcement.
Law enforcement provided Yahoo in November 2016 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. Based on further analysis of this data by the forensic experts, we believe an unauthorized third party, in August 2013, stole data associated with a broader set of user accounts, including yours. 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.
What Information Was Involved?
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. Not all of these data elements may have been present for your account. 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 we believe was affected.
What We Are Doing
We are taking action to protect our users:
We are requiring potentially affected users to change their passwords.
We invalidated unencrypted security questions and answers so that they cannot be used to access an account.
We continuously enhance our safeguards and systems that detect and prevent unauthorized access to user accounts.
What You Can Do
We encourage you to follow these security recommendations:
Change your passwords and security questions and answers for any other accounts on which you used the same or similar information used for your Yahoo account.
Review all of your accounts for suspicious activity.
Be cautious of any unsolicited communications that ask for your personal information or refer you to a web page asking for personal information.
Avoid clicking on links or downloading attachments from suspicious emails.
Additionally, please consider using Yahoo Account Key, a simple authentication tool that eliminates the need to use a password on Yahoo altogether.
For More Information
For more information about this issue and our security resources, please visit the Yahoo Security Issues FAQs page available at https://yahoo.com/security-update.
Protecting your information is important to us and we work continuously to strengthen our defenses.
Chief Information Security Officer