This is what happened. State sponsored hackers from Russia hacked into yahoo with a spear phishing method and stole data from billions. The stolen data was used to spy on certain targets in the U.S to gain economic and political advantages, which happened to include people with high power. They did this again in 2014 where they had gained over 500 million account keys.
The people who most likely did this are state sponsored hackers from Russia.
An unauthorized party stole data from Yahoo's servers. which included phone numbers, emails,
birthdates, and much more sensitive data. in 2014 hackers gained access to over 500 million account keys possibly using the same method.These attacks happened in 2013-2014.
Russia did this to gather political and economic intelligence to spy on certain targets in the U.S.
They likely used Spear phishing (sending a fraudulent email from a trusted sender) to carry out the attack.
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