The Yahoo hack occurred in 2013, the biggest known data breach suffered by a tech company, is bigger than originally stated. Verizon Communications, which acquired Yahoo for $4.48 billion in June, announced on Tuesday that the 2013 Yahoo hack affected all three billion of company user accounts. Last year, Yahoo declared that the incident affected one billion accounts, and it wasnt the unique incident suffered by the company. In 2014, hackers accessed 500 million accounts in a separate security breach. It is still unclear who is behind the attack, security experts attributed the 2013 hack to a Russian APT group.”]
Source: http://securityaffairs.co/wordpress/63813/cyber-crime/2013-yahoo-hack-3b-accounts.html