A judge on Monday ruled that Google’s ubiquitous search engine has been illegally exploiting its dominance to squash competition and stifle innovation in a seismic decision that could shake up the internet and hobble one of the world’s best-known companies.

The highly anticipated decision issued by U.S. District Judge Amit Mehta comes nearly a year after the start of a trial pitting the U.S. Justice Department against Google in the country’s biggest antitrust showdown in a quarter century.