BitTorrent is a protocol supporting the practice of peer-to-peer file sharing that is used to distribute large amounts of data over the Internet. BitTorrent is one of the most common protocols for transferring large files, and peer-to-peer networks have been estimated to collectively account for approximately 43% to 70% of all Internet traffic (depending on geographical location) as of February 2009. In November 2004, BitTorrent was responsible for 35% 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.
Programmer Bram Cohen, a former University at Buffalo graduate student in Computer Science, designed the protocol in April 2001 and released the first available version on July 2, 2001, and the final version in 2008. BitTorrent clients are available for a variety of computing platforms and operating systems including an official client released by Bittorrent, Inc.
As of 2009, BitTorrent reportedly had about the same number of active users online as viewers of YouTube and Facebook combined. As of January 2012, BitTorrent is utilized by 150 million active users (according to BitTorrent, Inc.). Based on this figure, the total number of monthly BitTorrent users can be estimated at more than a quarter of a billion.