A U.S. federal judge ruled Thursday that Google illegally maintained a monopoly over key parts of the digital advertising market, delivering a major setback to the tech giant.

Judge Leonie Brinkema found that Google engaged in anticompetitive practices to dominate publisher ad servers and ad exchanges, though she partially dismissed claims involving advertiser tools.

“Google has willfully engaged in a series of anticompetitive acts,” Brinkema wrote, adding that the conduct harmed rivals, publishers, and consumers.

The ruling stems from a lawsuit by the Justice Department and over a dozen states, which accused Google of using its dominance to suppress competition and inflate profits.

"Everyone from major news organizations to small independent bloggers has taken a financial hit because of Google’s conduct," said New York Attorney General Letitia James.

Google said it would appeal. “We won half of this case and we will appeal the other half,” said Lee-Anne Mulholland, Google’s VP of regulatory affairs.

Remedies could include forcing Google to divest parts of its ad business. A decision on next steps is expected within a week.

The ruling marks a significant moment in the government’s broader crackdown on Big Tech and could reshape the future of online advertising.