Alphabet's Google broke the law with an illegal monopoly on online search, a federal judge ruled on Monday, the first big win for U.S. antitrust authorities who have filed several lawsuits challenging Big Tech's market dominance. The ruling paves the way for a second trial to determine potential fixes, possibly including a breakup of Alphabet, that would change the landscape of the online advertising world that Google has dominated for years. It is also a green light to aggressive U.S. antitrust enforcers prosecuting Big Tech, which faces criticism from across the political spectrum.

In internal forecasts, the company projected that ad sales would keep declining, handing a tough challenge to its new chief executive.