A US judge has ruled that Google acted illegally to stifle competition and maintain its monopoly on online search and related advertising. This landmark decision, issued on Monday, represents a significant blow to Alphabet, Google's parent company, and could potentially reshape the tech industry.

The ruling follows a 2020 lawsuit filed by the US Department of Justice, which challenged Google's dominance, claiming it controls around 90% of the online search market. This case is part of a broader antitrust effort targeting major tech companies to enhance competition.

US District Judge Amit Mehta's decision describes Google as a monopolist that used billions of dollars to secure default search engine status on smartphones and browsers. He stated, “Google is a monopolist, and it has acted as one to maintain its monopoly.” The ruling suggests potential penalties, including the possibility of breaking up the company, although specifics will be decided in future hearings.

Alphabet plans to appeal, arguing that the decision undermines Google’s ability to offer its widely praised search engine. US Attorney General Merrick Garland lauded the ruling as a “historic win for the American people,” emphasizing that no company is above the law.

The case, which followed a 10-week trial, focused on Google's significant payments to companies like Apple and Samsung to be their default search engine. The Justice Department argued that these payments prevent other companies from competing effectively. Google countered that its search engine’s popularity is due to its quality and ongoing investment.

Another trial concerning Google’s advertising technology is set for September, while the company has faced substantial fines in Europe for similar monopoly violations.