BitTorrent is a communications protocol of peer-to-peer file sharing ("P2P") which is used to distribute data and electronic files over the Internet. BitTorrent is one of the most common protocols for transferring large files, such as digital video files containing TV shows or video clips or digital audio files containing songs. Peer-to-peer networks have been estimated to collectively account for approximately 43% to 70% of all Internet traffic (depending on location) as of February 2009. In November 2004, BitTorrent was responsible for 25% of all Internet traffic. As of February 2013, BitTorrent was responsible for 3.35% of all worldwide bandwidth, more than half of the 6% of total bandwidth dedicated to file sharing.
To send or receive files, a person uses a BitTorrent client on his or her Internet-connected computer. A BitTorrent client is a computer program that implements the BitTorrent protocol. Popular clients include μTorrent, Xunlei, Transmission, qBittorrent, Vuze, Deluge, BitComet and Tixati. BitTorrent trackers provide a list of files available for transfer, and allow the client to find peer users known as seeds who may transfer the files.
Programmer Bram Cohen, a former University at Buffalo student, designed the protocol in April 2001 and released the first available version on 2 July 2001, and the most recent version in 2013. BitTorrent clients are available for a variety of computing platforms and operating systems including an official client released by BitTorrent, Inc.
As of 2013, BitTorrent has 15–27 million concurrent users at any time. As of January 2012, BitTorrent is utilized by 150 million active users. Based on this figure, the total number of monthly BitTorrent users may be estimated to more than a quarter of a billion.