Meanwhile, Yahoo has admitted as many as 1 billion accounts were hacked in 2013. Yahoo says the hack involved private user information, including names, phone numbers, birthdates, passwords and security questions. In September, Yahoo also admitted that 500 million of its accounts were hacked in 2014. These two hacks are the largest known security breaches of a single company in history. Yahoo says it’s not known who is behind the newly disclosed hack.