Key facts
- Tokyo police said Yu Hai was arrested on November 7, 2026, allegedly operating a base station without a license.
- Police suspect an IMSI catcher forced nearby handsets onto an older 2G network before sending text messages.
- By the end of October, 18 people had contacted police reporting losses totaling about 4 million yen ($25,300).
- About 10,000 nearby cellphones lost service for one to two hours on days interfering signals were detected, per investigators.
- Yu has denied the allegations, police said, and told them he had never used radio equipment.
- Police said the case is Japan's first arrest over suspected interference with a carrier's radio communications.
Tokyo police referred Yu Hai, a 31-year-old unemployed Chinese national living in Tokyo's Kita ward, to prosecutors on November 9, 2026, for allegedly disrupting a major mobile carrier's services with a rogue cell tower device, police said. He was arrested on November 7, 2026, allegedly in the act of operating a base station without a license from a car parked on a Ginza street, an offense under Japan's Radio Law.
Police believe he used an IMSI catcher, a device that collects mobile phones' identifying numbers, to emit strong radio signals that forced nearby handsets onto an older 2G network before sending them text messages. Investigators suspect the messages, written in Chinese, posed as notices from Chinese banks and credit card companies asking recipients to enter card numbers and other personal information.
By the end of October, 18 Chinese nationals visiting or studying in Japan had contacted police about problems including unauthorized credit card use after accessing websites linked in the messages, police said. Reported losses totaled about 4 million yen ($25,300). Investigators said about 10,000 nearby cellphones lost service for one to two hours on days when such interfering signals were detected.
Signs of trouble emerged in December 2024, when a mobile carrier detected repeated disruptions in busy Tokyo areas and alerted police. In January 2025, police began receiving reports from Chinese tourists about suspicious texts and unauthorized charges. In May 2025, the communications ministry warned the public about suspected illegal radio equipment interfering with mobile services.
Yu has denied the allegations, police said. "I've never used radio equipment before. There was no radio equipment in the car, and I don't know anything about it," police quoted him as saying. Authorities said the case is Japan's first arrest over suspected interference with a mobile carrier's radio communications. IT journalist Yo Mikami said similar text messages have been reported across Japan, mainly in busy shopping and entertainment districts.