NEW YORK (WCMH/AP) – Yahoo confirms a huge data breach affecting 500 million accounts in what may be one of the largest cybersecurity breaches ever.

Yahoo says it believes a “state-sponsored actor” is behind the data breach. That means a hacker acting on behalf of a foreign government.

“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,” Yahoo said in a statement, adding that it is working closely with law enforcement on this matter.

The Yahoo accounts are said to be from those who used the service in late 2014. CNN reports the same hacker has previously claimed to sell stolen accounts from LinkedIn and MySpace.

Yahoo says it is working to contact all affected users. It is also urging all users to change their password and security questions and to review their accounts for suspicious activity.Keep checking for real-time updates on this story. To get alerts for breaking news, grab the free NBC4 News App for iPhone or Android. You can also sign up for email alerts.