Japanese authorities use new tool to identify initial torrent uploaders — anti-piracy group says it identified seeder on popular anime torrenting website without torrent swarm monitoring

In a recent development, Japanese authorities have employed a novel method to pinpoint the original uploaders of torrents. The Kyoto Prefectural Police recently apprehended Masakazu Ono, a 56-year-old resident of Sagamihara in Kamigawa Prefecture. This breakthrough was achieved through a multi-year investigation conducted by CODA, a Japanese anti-piracy organization, in collaboration with the Japan Hacker Association (JHA).

CODA's approach reportedly involved monitoring the trackers of the popular anime torrenting site Nyaa, rather than joining or observing the BitTorrent swarm traffic. This method allowed them to identify Ono as one of the initial seeders for the popular Japanese drama "Midnight Taxi," which was uploaded to Nyaa around 2026. CODA's investigation began in 2021 under the Cross-Border Enforcement Project, with the goal of identifying Nyaa's uploaders.

Over the course of three years, CODA and JHA gathered sufficient evidence to warrant the involvement of the Kyoto police in 2024. Three secondary uploaders from the same website were subsequently charged in 2025, presumably regular users who accessed the torrents through link aggregator sites. Typically, law enforcement agencies employ methods such as establishing a tracker honeypot or participating in the torrent swarm to identify file sharers.

However, Nyaa's tracker list is relatively small and consists of well-known, trusted servers. Consequently, it seems unlikely that these techniques were utilized in this case. Additionally, Japanese law generally discourages non-targeted data monitoring, making it less probable that techniques like Deep Packet Inspection (DPI) and traffic volume monitoring were employed until Ono's identification.