The RIAA’s big concern in the U.S. is PC users, who download music illegally, but apparently the bigger threat in Japan is people who download music to their mobile phone. And therefore, this week, the RIAJ announced that two men from Hyogo, Japan were taken into custody by police for running a mobile music download sites called “Daisan Sekai” (“The Third World”), reports ArsTechnica. The two had had no license to offer their tracks, although its unclear if they were doing it for profit, or merely hosting the download hub. The site attracted more than a million unique users, and the RIAJ considered it “one of the most popular illegal mobile music” sites in the country.