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 illegally dominates two markets for online advertising technology, a judge ruled on Thursday, dealing another blow to the tech giant and paving the way for U.S. antitrust prosecutors to seek a breakup of its ad products.

Google illegally acted to preserve “monopoly power” in the ad-tech business, a federal judge ruled Thursday. It’s the second antitrust case brought by the U.S. government that has gone against the internet giant in the past year.