By Bob Lord, CISO
We have confirmed that a copy of certain user account information was stolen from the company’s network in late 2014 by
what we believe is a state-sponsored actor. The account information may have included names, email addresses, telephone
numbers, dates of birth, hashed passwords (the vast majority with bcrypt) and, in some cases, encrypted or unencrypted
security questions and answers. The ongoing investigation suggests that stolen information did not include unprotected
passwords, payment card data, or bank account information; payment card data and bank account information are not stored
in the system that the investigation has found to be affected. Based on the ongoing investigation, Yahoo believes that
information associated with at least 500 million user accounts was stolen and the investigation has found no evidence
that the state-sponsored actor is currently in Yahoo’s network. Yahoo is working closely with law enforcement on this
We are taking action to protect our users:
• We are notifying potentially affected users. The content of the email Yahoo is sending to those users will be
available at https://yahoo.com/security-notice-content
beginning at 11:30 am (PDT).
• We are asking potentially affected users to promptly change their passwords and adopt alternate means of account
• We invalidated unencrypted security questions and answers so they cannot be used to access an account.
• We are recommending that all users who haven’t changed their passwords since 2014 do so.
• We continue to enhance our systems that detect and prevent unauthorized access to user accounts.
• We are working closely with law enforcement on this matter.
We encourage our users to follow these security recommendations
• Change your password and security questions and answers for any other accounts on which you used the same or similar
information used for your Yahoo account.
• Review 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 altogether.
An increasingly connected world has come with increasingly sophisticated threats. Industry, government and users are
constantly in the crosshairs of adversaries. Through strategic proactive detection initiatives and active response to
unauthorized access of accounts, Yahoo will continue to strive to stay ahead of these ever-evolving online threats and
to keep our users and our platforms secure.
For more information about this issue and our security resources, please visit the Yahoo Security Issue FAQs page, https://yahoo.com/security-update
, which will be up beginning at 12pm (PDT).
Statements in this press release regarding the findings of Yahoo’s ongoing investigation involve potential risks and
uncertainties. The final conclusions of the investigation may differ from the findings to date due to various factors
including, but not limited to, the discovery of new or additional information and other developments that may arise
during the course of the investigation. More information about potential risks and uncertainties of security breaches
that could affect the Company’s business and financial results is included under the caption “Risk Factors” in the
Company’s Quarterly Report on Form 10-Q for the quarter ended June 30, 2016, which is on file with the SEC and available
on the SEC’s website at http://www.sec.gov./