µTorrent (or uTorrent; commonly abbreviated as "µT" or "uT") is a freeware, closed source BitTorrent client now owned by BitTorrent, Inc. It is the most widely used BitTorrent client outside China (where Xunlei is more popular). It gets the "µ" in its name from the SI prefix "micro-", referring to the program's small memory footprint: the program was designed to use minimal computer resources while offering functionality comparable to larger BitTorrent clients such as Vuze or BitComet. The program has received consistently good reviews for its feature set, performance, stability, and support for older hardware and versions of Windows.
The program has been in active development since its first release in 2005. Although originally developed by Ludvig Strigeus, since December 7, 2006, the code is owned and maintained by BitTorrent, Inc. The code has also been employed by BitTorrent, Inc. as the basis for version 6.0 and above of the BitTorrent client, a re-branded version of µTorrent.
µTorrent is available for Microsoft Windows, Mac OS X and Linux. A µTorrent Server is also available for Linux. All versions are written in C++.
Early development
Out of general discontent with bloatware, Serge Paquet suggested to Ludvig Strigeusthat he should make a small and efficient BitTorrent client. Strigeus began to conceptualize the plans for the program's development, which, at the time, did not include making the client feature-rich. After initially working on it for about a month during the last quarter of 2004 (the first build is dated October 17, 2004), mostly during his free time before and after work, Strigeus ceased coding µTorrent for a year. He resumed work on September 15, 2005, and three days later, the first public release (version 1.1 beta) was made available as freeware, and began generating feedback.
PeerFactor SARL
On March 4, 2006, PeerFactor SARL announced the signing of a six-month contract with Strigeus for the development of "new content distribution applications on the Web." PeerFactor SARL is a relatively new company formed by former employees of PeerFactor, which was a subsidiary of the French anti-piracy organization Retspan.
Ludde stated that his coding for PeerFactor SARL was to use his expertise at optimization of the BitTorrent protocol to create a .dll which PeerFactor SARL intended to use as part of a distribution platform for files in a corporate setting. At the time there was some speculation that μTorrent may have been modified to spy on users on Peerfactor's behalf, however to date (even following μTorrent's acquisition by BitTorrent, Inc.) no evidence has been produced to support these allegations.
Ownership change
On December 7, 2006, µTorrent was purchased by BitTorrent, Inc., as it was announced on their official forum.
On September 18, 2007, BitTorrent 6.0 was released, which is a re-branded version of µTorrent. As a result, BitTorrent 6 is closed-source (unlike BitTorrent 5.x and before, which were open source software).
Magnet Link (URI) Support
Support for Magnet Links (URIs) was added in version 1.8, released on August 9, 2008. Magnet Links were designed as an alternative to traditional tracker torrent files and became popularized when sites such as The Pirate Bay included native support for the format.
Paid version
On July 15, 2011, BitTorrent announced that they would offer a paid version of µTorrent called "µTorrent Plus". This new version would offer extra features, such as integrated file conversion, anti-virus and a built in media player. On 6 October 2011, the Pre-alpha of µTorrent Plus was released to an invite only community. As of December 2011, µTorrentPlus 3.1 Stable is now available for purchase and download
