More than a decade since the heyday of Napster shareware, peer-to-peer file distribution remains a key tool for Internet users exchanging music and movie files online. The leading program in Japan is Winny, an application distributed free of charge since May 2002 by former University of Tokyo researcher Isamu Kaneko.

While Napster creator Shawn Fanning was hit with a series of lawsuits and taken to civil court by the music industry, Kaneko has faced criminal charges for allegedly encouraging Winny users to commit copyright infringement. The software also has been a reason for countless cases of data leaks, varying from private information on personal computers to internal government documents.

Winny most recently made headlines earlier this month, but this time for a controversial ruling by the Osaka High Court overturning a lower court judgment and acquitting Kaneko.