(Reuters) – Alphabet’s Google illegally dominated 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 advertising products.

U.S. District Judge Leonie Brinkema in Alexandria, Virginia, found Google liable for “willfully acquiring and maintaining monopoly power” in markets for publisher ad servers and the market for ad exchanges which sit between buyers and sellers. Publisher ad servers are platforms used by websites to store and manage their ad inventory.

Antitrust enforcers failed to prove a separate claim that the company had a monopoly in advertiser ad networks, she wrote.

Lee-Anne Mulholland, vice president of Regulatory Affairs, said Google will appeal the ruling.

“We won half of this case and we will appeal the other half,” she said, adding that the company disagrees with the decision on its publisher tools. “Publishers have many options and they choose Google because our ad tech tools are simple, affordable and effective.”

Google Shares Drop 2%

Google’s shares were down around 2.1% at midday.

The decision clears the way for another hearing to determine what Google must do to restore competition in those markets, such as sell off parts of its business at another trial that has yet to be scheduled.

The DOJ has said that Google should have to sell off at least its Google Ad Manager, which includes the company’s publisher ad server and ad exchange.

Google now faces the possibility of two U.S. courts ordering it to sell assets or change its business practices. A judge in Washington will hold a trial next week on the DOJ’s request to make Google sell its Chrome browser and take other measures to end its dominance in online search.

Google has previously explored selling off its ad exchange to appease European antitrust regulators, Reuters reported in September.

Brinkema oversaw a three-week trial last year on claims brought by the DOJ and a coalition of states.

Google used classic monopoly-building tactics of eliminating competitors through acquisitions, locking customers in to using its products, and controlling how transactions occurred in the online ad market, prosecutors said at trial.

Google argued the case focused on the past, when the company was still working on making its tools able to connect to competitors’ products. Prosecutors also ignored competition from technology companies including Amazon.com and Comcast as digital ad spending shifted to apps and streaming video, Google’s lawyer said.

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(Reporting by Jody Godoy in New York; Editing by Chizu Nomiyama and Richard Chang)