Context. Online piracy is widespread, controversial and poorly understood social phenomena that affects content creators, owners, and consumers. Online piracy, born from recent, rapid ITC changes, raises legal, ethical, and business challenges. Content owners, authors and content consumers should benefit from better understanding of online piracy. Improved, better adapted to marketplace and ITC changes content distribution models should benefit content owners and audiences.Objectives. Investigate online piracy effect on pirated product sales. Improve understanding of online piracy behaviors and process scale.Methods. This observational study investigated movie-sharing effect on U.S. box office. Movie sharing was observed over BitTorrent network, the most popular peer-to-peer file-sharing network. Relationship between piracy and sales was analyzed using linear regression model.Results. File sharing was found to have a slightly positive correlation with U.S. box office sales during first few weeks after film release, and no effect afterwards. Most of newly released movies are shared over BitTorrent network. File sharing is a global, massive phenomenon.Conclusions. I conclude that online movie file sharing has no negative correlation on U.S. box office. Slightly positive movie sharing correlation to box office sales could have occurred because sharing rather informs, than substitutes cinema going.