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.

It was the second time in a year that a U.S. court found that the company had acted illegally to remain dominant.

In another major legal blow to Google, a federal judge Thursday ruled that the search giant held an illegal monopoly over some advertising technology.