Yahoo says the personal information in 500 million accounts was stolen in a massive security breakdown. The breach disclosed Thursday, the latest setback for the beleaguered internet company, dates back to late 2014.

The stolen data includes users' names, email addresses, telephone numbers, dates of birth, hashed passwords and security questions for verifying an accountholder's identity. Yahoo is blaming the hack on a "state-sponsored actor."

The stolen data includes users' names, email addresses, telephone numbers, dates of birth, hashed passwords and security questions for verifying an accountholder's identify.

Yahoo is recommending that users change their passwords if they haven't done so since 2014.