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(NEW YORK) — Alphabet’s Google illegally dominated two markets for online advertising technology, according to a federal judge.

Judge Leonie Brinkema of the U.S. District Court for the Eastern District of Virginia said in a ruling Thursday that Google had broken the law to build its dominance over the largely invisible system of technology that places advertisements on pages across the web.

“Plaintiffs have proven that Google has willfully engaged in a series of anticompetitive acts to acquire and maintain monopoly power in the publisher ad server and ad exchange markets for open-web display advertising,” the judge wrote in his ruling. “For over a decade, Google has tied its publisher ad server and ad exchange together through contractual policies and technological integration, which enabled the company to establish and protect its monopoly power in these two markets.”

The Department of Justice had sued Alphabet claiming Google had a monopoly in ad technology that allowed the company to charge higher prices and take a bigger portion of each sale. The Justice Department has said Google should have to sell off at least its Google Ad Manager, which includes the company’s publisher ad server and its ad exchange.

“We won half of this case and we will appeal the other half,” Lee-Anne Mulholland, Google’s vice president for regulatory affairs, said in a statement. “The Court found that our advertiser tools and our acquisitions, such as DoubleClick, don’t harm competition. We disagree with the Court’s decision regarding our publisher tools. Publishers have many options and they choose Google because our ad tech tools are simple, affordable and effective.”

ABC News has reached out to Alphabet for comment.

Google is now facing the possibility of two different U.S. courts ordering it to sell assets or change its business practices. A trial will be held this April in Washington on the DOJ’s request to make Google sell its Chrome browser and take other measures to end its dominance in online search.

This is a developing story. Please check back for updates.