Oct. 27--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.

Following are questions and answers regarding Japan's most popular peer-to-peer program and the impact it is having on the country's online community:

What is Winny?

Winny is a file-sharing program that enables users to connect without using a central server.

The software makes it possible for computers connected to the Internet to exchange any digital data, including music, movies, computer software and other files.

Court documents say Kaneko has been interested in computers since he was in elementary school and as a researcher at the University of Tokyo he developed a variety of programs.

Napster, a program developed in the 1990s, kicked off the peer-to-peer file-sharing movement in the United States. But in Japan, it was Winny that started the ball rolling.

"There were file-sharing software programs prior to Winny, but Winny made its debut with a decentralized framework at a time when the crackdown on copyright infringement was beginning," said Toshinao Sasaki, a noted journalist and author of "The Study Guide of the Internet Industry."

It was automatic after that, as the program spread like a virus. The vast amount of shared files on the network created a synergistic effect that attracted thousands of new users, making Winny the standard in Japan.

How many people download files through Winny?

A survey of 20,350 people released by the Association of Copyright for Computer Software in Japan in September 2008 revealed that 10.3 percent of computer users were using file-sharing software, the first time it was more than 10 percent since the survey began in 2002.

It found that 58 percent of file sharers exchange music online, 27.4 percent swap movies, and 21.6 percent use it to download pornography.