Yahoo has disclosed that it was the victim of a hack attack back in 2013 which resulted in the theft of personal information related to more than 1 billion users. The stolen data included names, email addresses, telephone numbers, dates of birth and passwords. The company discovered the breach while investigating a separate 2014 attack which had been considered the biggest theft of personal data in history. That attack affected around 500 million users. The 2014 attack has been attributed to a nation-state, but Yahoo doesn't yet know who was behind the 2013 attack.
The attack casts doubt on Verizon's plans to buy some of Yahoo's core Internet assets.
Yahoo is recommending that all users change their passwords.