Google has illegally built “monopoly power” with its web advertising business, a federal judge in Virginia has ruled, siding with the Justice Department in a landmark case against the tech giant that could reshape the basic economics of running a modern website.

Alphabet Inc.’s Google has been found by two federal judges, in less than a year, to have illegally monopolized critical parts of the internet.

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