Yahoo says hackers stole information in what is apparently the biggest publicly revealed cyber-breach ever.
The breach included swathes of personal information, including e-mails and names, in addition to “unencrypted security questions and answers”.
The hack occurred in 2014 but has only now been made public.
Yahoo said it believed the assault was state- sponsored.
The data taken contains dates of birth, names, email addresses, telephone numbers and encrypted passwords, but not credit card info, Yahoo said.
News of a potential major assault on the technology company emerged in August when a hacker called “Peace” was obviously trying to sell advice on 200 million Yahoo accounts.
On Thursday, Yahoo confirmed the breach was much bigger than first thought.
Yahoo is urging all users should change their passwords if they never have done since 2014.