µTorrent (or uTorrent and commonly abbreviated as "µT" or "uT") is a freeware, closed source BitTorrent client by BitTorrent, Inc. It is available for Microsoft Windows and Mac OS X. Both versions are written in C++. It gets the "µ" in its name from the SI prefix "micro" meaning one one-millionth and it refers to the program's small footprint. The program is 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. A report showed that µTorrent is the second most popular BitTorrent client (after the Chinese Xunlei).
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 of the BitTorrent client, a re-branded version of µTorrent.
According to a study by Arbor Networks, the 2008 adoption of IPv6 by µTorrent caused a 15-fold increase in IPv6 traffic across the internet over a ten month period.