CIO: One mistaken click. That's all it took for hackers aligned with the Russian state security service to gain access to Yahoo's network and potentially the email messages and private information of as many as 500 million people.
The U.S. Federal Bureau of Investigation has been investigating the intrusion for two years, but it was only in late 2016 that the full scale of the hack became apparent. On Wednesday, the FBI indicted four people for the attack, two of whom are Russian spies.
Here's how the FBI says they did it: