A US federal judge has ruled that Google holds an illegal monopoly in the digital advertising technology sector, marking another major setback for the tech giant in a growing wave of antitrust challenges.

The decision comes after the US Department of Justice and 17 states filed a lawsuit accusing Google of unlawfully dominating the digital tools that determine how online ads are placed and distributed.

This is the second time within a year that Google has been found guilty of monopolistic practices—following a previous ruling that concluded the company had a monopoly in online search.

Google said it would appeal against the decision, reports BBC.

In response, Google has vowed to appeal the latest ruling. Lee-Ann Mulholland, Google’s head of regulatory affairs, defended the company’s practices, stating, “Publishers have many choices, and they choose Google because our tools are effective, affordable, and easy to use.”

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However, US District Judge Leonie Brinkema stated in her ruling that Google had “wilfully engaged in a series of anticompetitive acts” to gain and maintain dominance in the online advertising market. She emphasised that such behavior harmed not only Google’s publishing clients but also damaged market competition and ultimately impacted consumers.

The court found Google guilty on two counts related to monopolistic behavior, while a third allegation was dismissed. Mulholland highlighted the partial win, saying, “We won half of this case and will appeal the other half,” and pointed out that the court did not find Google's acquisitions, such as DoubleClick, to be harmful to competition.