PRAGUE — A Russian man accused of hacking the systems of three American technology companies in 2012, possibly compromising the personal information of more than 100 million users, was extradited to the United States from the Czech Republic on Friday.

The man, Yevgeniy A. Nikulin, appeared in Federal District Court in San Francisco after arriving in the city around 6 a.m. He pleaded not guilty to the charges against him. Magistrate Judge Jacqueline Scott Corley scheduled his next court appearance for next week.

“This is deeply troubling behavior once again emanating from Russia,” Attorney General Jeff Sessions said in a statement. “We will not tolerate criminal cyberattacks and will make it a priority to investigate and prosecute these crimes, regardless of the country where they originate.”

Mr. Nikulin had been held in the Czech Republic since the authorities there arrested him in 2016. His case quickly turned into a battle between Washington and Moscow over whether he should be tried in the United States.