The future of Google's advertising business is at stake after a federal judge found the company illegally monopolized parts of it.

The ruling was the second time in a year that a federal court had found that Google had acted illegally to maintain its dominance.

A U.S. judge's ruling that Google has illegal monopolies in ad technology sets up the possibility of U.S. prosecutors seeking a breakup. Here's what the case involves and what Google owner Alphabet faces from here.