A lot of the story regarding the Tetris split between Nintendo and Tengen is covered in the great Gaming Historian video [The Story of Tetris](https://www.youtube.com/watch?v=_fQtxKmgJC8&t=1s).
There's another episode from Gaming Historian specifically for Tengen:
https://www.youtube.com/watch?v=fLA_d9q6ySs
It talks about how Atari abuses the copyright system to gain access to Nintendo’s protection system source code.
Hacked not abused. Nintendo abused the copyright system to lock out cartridges.
Nope, while Nintendo definitely abused copyright law doesn't mean Atari/Tengen is in the clear. They specifically requested the lockout code fron the US Copyright Office under the pretense that they'll be suing Nintendo.