Williams Electronics, Inc. v. Artic International, Inc.
Place your cursor over the image to see just how identical Defender and Defense Command are.
This case involves copying the arcade video game Defender, one of the most popular video games of all time. The plot is that you pilot a spaceship trying to stop aliens from abducting humans. It is estimated that people have spent over $1 billion playing the game. With such success, it's not surprising that other companies wanted to replicate the game. Defense Command, however, was not the only Defender-clone. Both Mayday!! and Mirage are also considered to be virtual copies.
You can play Defender online for free on archive.org. As a side note, the man who created Defender, Eugene Jarvis, is still creating video games today, 25 years later.