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's Google plans to appeal against the "adverse" portion of the court decision in the U.S. Department of Justice’s monopoly case against the technology giant.

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