Hackers breached Yahoo's networks and gained access to one billion user accounts, which included phone numbers, addresses, and easily cracked hashed passwords.
The released data also included certain encrypted and cleartext security questions and answers that had also been compromised. The passwords were secured with the easily cracked MD5 hashing method.
According to more information about the incident, the hacker sold the enormous data collection on the Dark Web.
Unfortunately, the hacker was paid by at least three distinct buyers two of whom were prominent spammers to obtain the complete information, which they most certainly intended to exploit for espionage purposes.
Source: https://securityaffairs.com/54486/data-breach/yahoo-data-dark-web.html
"id": "YAH35131123",
"linkid": "yahoo",
"type": "Breach",
"date": "12/2016",
"severity": "100",
"impact": "",
"explanation": "Attack threatening the organization's existence"