1. 2014 Breach: In 2014, Russian state-sponsored cybercriminals were widely believed to be responsible for a massive cyberattack on Yahoo. The hackers managed to steal sensitive information from over 500 million Yahoo user accounts, including email addresses, phone numbers, birth dates, and encrypted passwords.

2. 2016 Additional Breaches: In 2016, further investigations revealed two more significant breaches of Yahoo's systems. Unlike the 2014 attack attributed to Russian hackers, the U.S. government believed that a Chinese state-sponsored hacking group was likely behind these subsequent breaches.

Why:

Espionage and Financial Gain: The Russian hackers involved in the 2014 attack are generally motivated by espionage and stealing valuable information for their government's benefit. For the Chinese hackers behind the 2016 breaches, the primary objective is often economic espionage and intellectual property theft, benefiting their country's commercial and technological interests.