Yahoo"s CISO blames a state-sponsored actor for the biggest breach in the company's history

Yahoo”s Chief Information Security Officer, Bob Lord, confirmed in an e-mail sent Thursday night to Yahoo users that hackers stole information from at least 500 million user accounts.

Lord explains that “a copy of certain user account information was stolen from our systems in late 2014 by what we believe is a state-sponsored actor.” The company is now “closely” coordinating with law enforcement on this matter and working diligently to protect you.

“The stolen user 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,” he added. “Not all of these data elements may have been present for your account. 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 found to be affected.”

The measures Yahoo will take to protect users:

• Yahoo is asking potentially affected users to promptly change their passwords and adopt alternate means of account verification.
• Yahoo invalidated unencrypted security questions and answers so they cannot be used to access an account.
• Yahoo is recommending that all users who haven’t changed their passwords since 2014 do so.
• Yahoo continues to enhance their systems that detect and prevent unauthorized access to user accounts.
• Yahoo is working closely with law enforcement on this matter.

What users can do:

• Change your password and security questions 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, users may consider using Yahoo Account Key, an authentication tool that eliminates the need to use a password altogether.