A federal judge ruled on Monday that Google illegally maintained a monopoly in search, saying in the landmark case that the tech giant paid companies to make Google the default search engine on smartphones and other devices. The case has the potential to change how tech companies do business, as well as how their customers find answers to their online search queries. The trial, held last year, took 10 weeks and was years in the making.

"After having carefully considered and weighed the witness testimony and evidence, the court reaches the following conclusion: Google is a monopolist, and it has acted as one to maintain its monopoly," US District Judge Amit Mehta wrote in the decision. "It has violated Section 2 of the Sherman Act."

Why is this so important?

The ruling comes as Big Tech is seeing renewed scrutiny from regulators both domestically and abroad. Apple was hit with an antitrust suit by the US Department of Justice and 16 state attorneys general earlier this year that accused the iPhone maker of having too tight of a control on its premium handset, preventing other companies from creating applications that could compete with its own. 

Amazon, too, was hit with a lawsuit by the US Federal Trade Commission and 17 state attorneys general last year that alleged the online retail giant engages in exclusionary and anticompetitive behavior. And, per the EU's Digital Markets Act, Apple had to allow third-party app stores to work with iPhone. Google itself has been embroiled in a number of lawsuits, including one involving data handling in its Chrome browser.

Google is currently the king of online search, with over 91% global market share, according to GlobalStats. 

What's next for Google?

Mehta's ruling didn't include potential remedies for Google's behavior. His decision in that regard could force the company to change how it operates or even sell off part of the company. 

Google said it plans to appeal the ruling.

"This decision recognizes that Google offers the best search engine, but concludes that we shouldn't be allowed to make it easily available," Kent Walker, the company's president for global affairs, said in a statement.

He went on to cite numerous instances of praise for Google's search engine, quoting directly from the 277-page decision, which has been shared online by The New York Times.

"We appreciate the Court's finding that Google is 'the industry's highest quality search engine, which has earned Google the trust of hundreds of millions of daily users,' that Google 'has long been the best search engine, particularly on mobile devices,' 'has continued to innovate in search' and that 'Apple and Mozilla occasionally assess Google's search quality relative to its rivals and find Google's to be superior,'" Walker said. "Given this, and that people are increasingly looking for information in more and more ways, we plan to appeal. As this process continues, we will remain focused on making products that people find helpful and easy to use."

The Justice Department didn't immediately respond to a request for comment.

New York Attorney General Letitia James, one of the attorneys general involved in bringing the suit, tweeted about the case on X. James called the case a "major victory to stop unchecked corporate power from stifling competition and controlling our data and privacy."

And at least one competing search engine company representative weighed in.

"Google has used its monopoly power to block meaningful competition in the search market by putting a stranglehold on major distribution points for more than a decade," said Kamyl Bazbaz, a senior vice president at DuckDuckGo. "So even though DuckDuckGo provides something valuable that people want and Google won't provide -- real privacy protection online -- Google makes it difficult to use DuckDuckGo by default. We applaud this landmark decision and the important work of the Department of Justice and state Attorneys General to enforce our antitrust laws."

DuckDuckGo has positioned itself as a privacy-focused alternative to Google.

Do users switch from default search engines?

The Google case focused on whether Google paid Apple and other companies to make its search engine the default on devices such as Apple's iPhone. Google has said it didn't maintain a monopoly through use of such agreements and that consumers could change their device defaults to use other search engines. 

Microsoft CEO Satya Nadella testified in October that the idea that users shift from one search engine to another was "completely bogus" and added  "defaults is the only thing that matters in changing search behavior."

According to the Justice Department, the Google search engine is used for nearly 90% of web searches, but the company disputes that number, the Times reports.

The Sherman Antitrust Act, which dates back to 1890, prohibits activities that restrict interstate commerce and competition in the marketplace, essentially outlawing corporate monopolies. It's considered the cornerstone of US antitrust legislation, leading to the federal government's breakup of late 19th century Gilded Age industrial giants.

CNET's Imad Khan contributed to this report.