Winny is a file-sharing program that allows users to search and exchange such media as movies, television shows and games saved on the hard drives of personal computers. Winny transfers requested files through multiple computers, leaving a copy in each intermediate host. The sender and requester of a file remain anonymous, and the accessed IP (Internet Protocol) addresses are encrypted, making it difficult to identify users. The program, which first appeared in 2002 as freeware, has been upgraded more than 200 times to enhance its functions.

Winny (also known as WinNY) is a Japanese peer-to-peer (P2P) file-sharing program that claims to be loosely inspired by the design principles behind the Freenet network and that also claimed to keep user identities untraceable. While Freenet was implemented in Java, Winny was implemented as a Windows C++ application.