Yahoo has the dubious distinction of having the two largest data breaches in history. The first was disclosed in September 2016, affecting 500 million accounts. The second was made public only three months later when the company announced that there was a separate breach, believed to be committed by different actors, affecting 1 billion accounts. Making matters even worse? The first breach occurred in 2014, while the second happened in 2013. It's still unclear why Yahoo did not detect either intrusion until years after the fact.