Google illegally monopolized some online advertising technology markets, according to a federal judge, whose ruling marked the latest antitrust setback for the company and a challenge to its main source of revenue.

The tech giant faces multiple legal threats related to how it wields market power.

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.