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BitTorrent Addresses Closed Source Issues
August 8, 2007
Thomas Mennecke
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Update: There appears to have been some confusion on the exact documentation status of the BitTorrent protocol. The protocol will continue to be published on and will continue to be available for everyone who's interested to see. It will not be closed or require a special SDK license to obtain the latest specifications. Additionally, BitTorrent will continue to update the site with the latest specifications.

BitTorrent gained prominence in the file-sharing community largely due to its open source nature. What began as an unknown file-sharing client quickly diversified into a vast collection of applications. Developers were able to take the original BitTorrent source code and forge their own creations. The result of this ability includes the development of Azurues, BitComet, Transmission, and of course, uTorrent (micro Torrent).

The mainline BitTorrent client had some following, however never came close to the consumer penetration of uTorrent or Azureus. With its nearly 17 million users, fully functional user interface, low memory footprint and nearly indistinguishable CPU consumption, the closed source uTorrent became an attractive target for BitTorrent, Inc. On December 7, 2006, Bram Cohen, CEO or BitTorret, and Ludvig (Ludde) Strigeus, developer of uTorrent, formally announced BitTorrent, Inc.'s acquisition.

It was reasonably assumed that not a whole lot was going to change after the acquisition. Bram Cohen had assured everyone that the community experience surrounding uTorrent would remain intact.

"What does this mean for the uTorrent community? Not much, at least not at first. The intention is to maintain the website as it is, and keep the forums and community active."

That's all good and well, but the primary concern revolves around the open source nature of the BitTorrent protocol. The BitTorrent protocol is, or at least was, open prior to uTorrent becoming the official client (BitTorrent version 6.0). With uTorrent primed to become the official client, many were concerned that the BitTorrent protocol would become closed. According to the uTorrent acquisition FAQ, this concern was addressed directly.

"Q: How will this impact the BitTorrent open source development community as a whole?

A: There will be no impact to the BitTorrent open source development community. We are committed to maintaining the preeminent reference implementation of BitTorrent under an open source license."

BitTorrent 6.0, the official mainline client based on uTorrent, was released on July 28, 2006. Unlike previous official releases, there was no corresponding source code. While it's understandable that uTorrent's code may not be released, concerns remain that the protocol may advance while leaving the open source community behind.

"Sorry, source code for BitTorrent 6.0, like the source code for uTorrent, will not be released. However, versions 5 and earlier were of course released under open source licenses, and remain available for you to modify and redistribute subject to the terms of their respective licenses."

It's true enough that earlier versions of the BitTorrent protocol are available, however considering that BitTorrent is continuously evolving, older versions offer little benefit to a forward looking developer. To many in the BitTorrent community, BitTorrent, Inc. has turned its back on the open source movement. Addressing these concerns, Ashwin Navin, President of BitTorrent, Inc., spoke to

"That's a true statement," Ashwin told, referring to the uTorrent acquisition FAQ. "We'll always maintain an open source version, although it may not necessarily reflect the latest client on the site."

There are two aspects to the BitTorrent open source debate - the protocol itself, and the client. What helped motivate BitTorrent's decision to close the mainline client?

"There are two issues people need to come to grips with. Developers who produce open source products will often have their product repackaged and redistributed by businesses with malicious intent. They repackage the software with spyware or charge for the product. We often receive phone calls from people who complain they have paid for the BitTorrent client."

As a company that distributes a free product, no one should ever have to pay for the BitTorrent client. Ashwin told that by keeping the source closed, it creates a "certain amount of distinction" between the official client and maliciously repackaged software.

Considering that uTorrent has always been closed source, these facts may not upset too many people. uTorrent became the single most popular BitTorrent client, despite its closed source nature. Yet there's still one remaining issue, that being the protocol.

With previous versions (prior to 6.0), the protocol was just as open as the old mainline client. This has changed with the release of 6.0. Developers, community members and newcomers to the BitTorrent scene have expressed concern that keeping up with the latest protocol developments may be difficult, if not impossible.

However this will not be the case, as the protocol will continue to be maintained at

While the BitTorrent client and the latest protocol may not be published, therefore technically closed source, the protocol is still open. The details of the protocol extensions, including all the latest revisions, are still available to whoever wants them. BitTorrent's recent move isn't going to make everyone happy, but those wishing to help develop the BitTorrent community probably won't notice much of a difference.

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BitTorrent :: BitTorrent Inc.

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