It appears that about millions of users were affected by the 2014 attack on Yahoo’s servers. The company claim that state sponsored hackers were behind the data breach – was rejected by security firms. The massive incident, so it seems, was carried out by a group of hackers called “Group E” based on eastern europe, which work with spammers.
The data that Group E had were: user id, password, phone number and zip code. They sold the information