A massive breach of Yahoo s systems in 2013 impacted every account in existence at the time, the company said last night in a new filing with the Securities and Exchange Commission. The 2013 breach was one of two disclosed by Yahoo last year; the second occurred in 2014 when hackers walked off with a half-billion account records. The attackers made off with names, email addresses, telephone numbers and some dates of birth, hashed hashed data. The 2014 breach was disclosed in September 2016; Congress then demanded answers from CEO Marissa Mayer.
Source: https://threatpost.com/2013-yahoo-breach-affected-all-3-billion-accounts/128259/