SAN FRANCISCO — Hackers are discovering that it is far more profitable to hold your data hostage than it is to steal it.

A decade-old internet scourge called ransomware went mainstream on Friday when cybercriminals seized control of computers around the world, from the delivery giant FedEx in the United States to Britain’s public health system, universities in China and even Russia’s powerful Interior Ministry.

On Saturday, investigators could not yet tell who was behind the attack as security experts around the world raced to contain it. Across Asia, several universities and organizations said they had been affected. Renault, the European automaker, said on Saturday that its French operations had been hit, while one of its plants in Slovakia was shut down because of the digital outbreak.

Computer users in the United States so far were less affected after a 22-year-old British cybersecurity researcher inadvertently stopped the ransomware attack from spreading more widely.