The Pirate Bay allows users to search for Magnet links. These are used to reference resources available for download via peer-to-peer networks which, when opened in a BitTorrent client, begin downloading the desired content. (Originally, The Pirate Bay allowed users to download BitTorrent files (torrents), small files that contain metadata necessary to download the data files from other users). The torrents are organised into categories: "Audio", "Video", "Applications", "Games", "Porn" and "Other". Registration requires an email address and is free; registered users may upload their own torrents and comment on torrents. According to a study of newly uploaded files during 2013 by TorrentFreak, 44% of uploads were television shows and movies, porn was in second place with 35% of uploads, and audio made up 9% of uploads.