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.

A federal judge has found that Google violated antitrust laws by “willfully acquiring and maintaining monopoly power” in the advertising technology