Peer-to-peer file sharing

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Peer-to-peer file sharing is the distribution and sharing of digital media using peer-to-peer (P2P) networking technology. P2P file sharing allows users to access media files such as books, music, movies, and games using a P2P software program that searches for other connected computers on a P2P network to locate the desired content. [1] The nodes (peers) of such networks are end-user computers and distribution servers (not required).

Digital media any media that are encoded in machine-readable formats

Digital media are any media that are encoded in machine-readable formats. Digital media can be created, viewed, distributed, modified and preserved on digital electronics devices.

Peer-to-peer Type of decentralized and distributed network architecture

Peer-to-peer (P2P) computing or networking is a distributed application architecture that partitions tasks or workloads between peers. Peers are equally privileged, equipotent participants in the application. They are said to form a peer-to-peer network of nodes.

File sharing is the practice of distributing or providing access to digital media, such as computer programs, multimedia, documents or electronic books. File sharing may be achieved in a number of ways. Common methods of storage, transmission and dispersion include manual sharing utilizing removable media, centralized servers on computer networks, World Wide Web-based hyperlinked documents, and the use of distributed peer-to-peer networking.


Peer-to-peer file sharing technology has evolved through several design stages from the early networks like Napster, which popularized the technology, to the later models like the BitTorrent protocol. Microsoft uses it for Update distribution (Windows 10) and online playing games (e.g. the mmorpg Skyforge [2] ) use it as their content distribution network for downloading large amounts of data without incurring the dramatic costs for bandwidth inherent when providing just a single source.

Napster is a set of three music-focused online services. It was founded as a pioneering peer-to-peer (P2P) file sharing Internet software that emphasized sharing digital audio files, typically audio songs, encoded in MP3 format. As the software became popular, the company ran into legal difficulties over copyright infringement. It ceased operations and was eventually acquired by Roxio. In its second incarnation, Napster became an online music store until it was acquired by Rhapsody from Best Buy on December 1, 2011.

Massively multiplayer online role-playing games (MMORPGs) are a combination of role-playing video games and massively multiplayer online games in which a very large number of players interact with one another within a virtual world.

Skyforge is a free-to-play massively multiplayer online role-playing game developed by Allods Team in collaboration with Obsidian Entertainment, and published by Set on the planet Aelion, Skyforge fuses elements of science-fiction and fantasy in its visuals and storytelling, and sees players exploring the world as an immortal who must strive to become a god. The project started development in 2010 and received an open release for Microsoft Windows in July 2015, with PlayStation 4 and Xbox One releases following in 2017. The latest big content update, New Horizons, was released on all platforms in April 2019.

Several factors contributed to the widespread adoption and facilitation of peer-to-peer file sharing. These included increasing Internet bandwidth, the widespread digitization of physical media, and the increasing capabilities of residential personal computers. Users are able to transfer one or more files from one computer to another across the Internet through various file transfer systems and other file-sharing networks. [1]

File transfer is the transmission of a computer file through a communication channel from one computer system to another. Typically, file transfer is mediated by a communications protocol. In the history of computing, numerous file transfer protocols have been designed for different contexts.


Peer-to-peer file sharing became popular with the introduction of Napster, a file sharing application and a set of central servers that linked people who had files with those who requested files. The central index server indexed the users and their shared content. When someone searched for a file, the server searched all available copies of that file and presented them to the user. The files would be transferred directly between the two private computers. A limitation was that only music files could be shared. [3] Because this process occurred on a central server, however, Napster was held liable for copyright infringement and shut down in July 2001. It later reopened as a pay service. [4]

After Napster was shut down, the most popular peer-to-peer services were Gnutella and Kazaa. These services also allowed users to download files other than music, such as movies and games. [3]

Gnutella is a large peer-to-peer network. It was the first decentralized peer-to-peer network of its kind, leading to other, later networks adopting the model. It celebrated a decade of existence on March 14, 2010, and has a user base in the millions for peer-to-peer file sharing.

Kazaa peer-to-peer file sharing application

Kazaa Media Desktop started as a peer-to-peer file sharing application using the FastTrack protocol licensed by Joltid Ltd. and operated as Kazaa by Sharman Networks. Kazaa was subsequently under license as a legal music subscription service by Atrinsic, Inc. According to one of its creators, Jaan Tallinn, Kazaa is pronounced ka-ZAH.

Technology evolution

Napster and eDonkey2000, which both used a central server-based model, may be classified as the first generation of P2P systems. [5] These systems relied on the operation of the respective central servers, and thus were susceptible to centralized shutdown. The second generation of P2P file sharing encompasses networks like Kazaa, Gnutella and Gnutella2, which are able to operate without any central servers, eliminated the central vulnerability by connecting users remotely to each other. [6]

eDonkey2000 peer-to-peer file sharing application

eDonkey2000 was a peer-to-peer file sharing application developed by US company MetaMachine, using the Multisource File Transfer Protocol. This client supports both the eDonkey2000 network and the Overnet network.

Gnutella2, often referred to as G2, is a peer-to-peer protocol developed mainly by Michael Stokes and released in 2002.

The third generation of filesharing networks are the so-called darknets, including networks like Freenet, which provide user anonymity in addition to the independence from central servers. [7]

The BitTorrent protocol represents a special case. In principle, it is a filesharing protocol of the first generation, relying on central servers called trackers to coordinate users. However, it does not form a network in the traditional sense. Instead new, separate networks of coordinating users are created for every set of files, called a torrent. Newer extensions of the protocol removes the need of centralized trackers, allow the usage of a decentralized server-independent network for source identification purposes, referred to as the Mainline DHT. This allows BitTorrent to encompass certain aspects of a filesharing network of the second generation as well. Users create an index file containing the metadata of the files they want to share, and upload the index files to websites where they are shared with others.

Peer-to-peer file sharing is also efficient in terms of cost. [8] [9] The system administration overhead is smaller because the user is the provider and usually the provider is the administrator as well. Hence each network can be monitored by the users themselves. At the same time, large servers sometimes require more storage and this increases the cost since the storage has to be rented or bought exclusively for a server. However, usually peer-to-peer file sharing does not require a dedicated server. [10]

Economic impact

There is still ongoing discussion about the economic impact of P2P file sharing. Norbert Michel, a policy analyst at the Heritage Foundation, said that because of "econometric and data issues, studies thus far have produced disparate estimates of file sharing's impact on album sales." [11]

In the book The Wealth of Networks , Yochai Benkler states that peer-to-peer file sharing is economically efficient and that the users pay the full transaction cost and marginal cost of such sharing even if it "throws a monkey wrench into the particular way in which our society has chosen to pay musicians and re-cording executives. This trades off efficiency for longer-term incentive effects for the recording industry. However, it is efficient within the normal meaning of the term in economics in a way that it would not have been had Jack and Jane used subsidized computers or network connections". [12]

As peer-to-peer file sharing can be used to exchange files for which the distribution right was granted (e.g. public domain, Creative Commons, Copyleft licenses, online games, updates, ...).

Especially startups can save massive amounts of money compared with other means of content delivery networks.

A calculation example:

with peer to peer file sharing:

with casual content delivery networks:

Music industry

The economic effect of copyright infringement through peer-to-peer file sharing on music revenue has been controversial and difficult to determine. Unofficial studies found that file sharing had a negative impact on record sales. [13] [14] [15] [16] [17] It has proven difficult to untangle the cause and effect relationships among a number of different trends, including an increase in legal online purchases of music; illegal file-sharing; drops in the prices of CDs; and the extinction of many independent music stores with a concomitant shift to sales by big-box retailers. [18]

Also many independent artists choose a peer-to-peer file sharing method named BitTorrent Bundle for distribution.

Film industry

The MPAA reported that American studios lost $2.373 billion to Internet piracy in 2005, representing approximately one third of the total cost of film piracy in the United States. [19] The MPAA's estimate was doubted by commentators since it was based on the assumption that one download was equivalent to one lost sale, and downloaders might not purchase the movie if illegal downloading was not an option. [20] [21] [22] Due to the private nature of the study, the figures could not be publicly checked for methodology or validity, [23] [24] [25] and on January 22, 2008, as the MPAA was lobbying for a bill which would compel universities to crack down on piracy, it was admitted by MPAA that its figures on piracy in colleges had been inflated by up to 300%. [26] [27]

A 2010 study, commissioned by the International Chamber of Commerce and conducted by independent Paris-based economics firm TERA, estimated that unlawful downloading of music, film and software cost Europe's creative industries several billion dollars in revenue each year. [28] Furthermore, the TERA study entitled "Building a Digital Economy: The Importance of Saving Jobs in the EU's Creative Industries" predicted losses due to piracy reaching as much as 1.2 million jobs and €240 billion in retail revenue by 2015 if the trend continued. Researchers applied a substitution rate of ten percent to the volume of copyright infringements per year. This rate corresponded to the number of units potentially traded if unlawful file sharing were eliminated and did not occur. [29] Piracy rates of one-quarter or more[ vague ] for popular software and operating systems have been common, even in countries and regions with strong intellectual property enforcement, such as the United States or the EU. [30]

Public perception and usage

In 2004, an estimated 70 million people participated in online file sharing. [31] According to a CBS News poll, nearly 70 percent of 18- to 29-year-olds thought file sharing was acceptable in some circumstances and 58 percent of all Americans who followed the file sharing issue considered it acceptable in at least some circumstances. [32]

In January 2006, 32 million Americans over the age of 12 had downloaded at least one feature-length movie from the Internet, 80 percent of whom had done so exclusively over P2P. Of the population sampled, 60 percent felt that downloading copyrighted movies off the Internet did not constitute a very serious offense, however 78 percent believed taking a DVD from a store without paying for it constituted a very serious offense. [33]

In July 2008, 20 percent of Europeans used file sharing networks to obtain music, while 10 percent used paid-for digital music services such as iTunes. [34]

In February 2009, a Tiscali UK survey found that 75 percent of the English public polled were aware of what was legal and illegal in relation to file sharing, but there was a divide as to where they felt the legal burden should be placed: 49 percent of people believed P2P companies should be held responsible for illegal file sharing on their networks, 18 percent viewed individual file sharers as the culprits, while 18 percent either didn't know or chose not to answer. [35]

According to an earlier poll, 75 percent of young voters in Sweden (18-20) supported file sharing when presented with the statement: "I think it is OK to download files from the Net, even if it is illegal." Of the respondents, 38 percent said they "adamantly agreed" while 39 percent said they "partly agreed". [36] An academic study among American and European college students found that users of file-sharing technologies were relatively anti-copyright and that copyright enforcement created backlash, hardening pro-file sharing beliefs among users of these technologies. [37]

Communities in P2P file sharing networks

Communities have a prominent role in many peer to peer networks and applications, such as BitTorrent, Gnutella and DC++. There are different elements that contribute to the formation, development and the stability of these communities, which include interests, user attributes, cost reduction, user motivation and the dimension of the community.

Interest attributes

Peer communities are formed on the basis of common interests. For Khambatti, Ryu and Dasgupta common interests can be labelled as attributes "which are used to determine the peer communities in which a particular peer can participate". [38] There are two ways in which these attributes can be classified: explicit and implicit attributes.

Implicit values means that peers provide information about themselves to a specific community, for example they may express their interest in a subject or their taste in music. With explicit values, users do not directly express information about themselves, albeit, it is still possible to find information about that specific user by uncovering his or her past queries and research carried out in a P2P network. Khambatti, Ryu and Dasgupta divide these interests further into three classes: personal, claimed and group attributes. [38]

A full set of attributes (common interests) of a specific peer is defined as personal attributes, and is a collection of information a peer has about him or herself. Peers may decide not to disclose information about themselves to maintain their privacy and online security. It is for this reason that the authors specify that "a subset of...attributes is explicitly claimed public by a peer", and they define such attributes as "claimed attributes". [38] The third category of interests is group attributes, defined as "location or affiliation oriented" and are needed to form a...basis for communities", an example being the "domain name of an internet connection" which acts as an online location and group identifier for certain users.

Cost reduction

Cost reduction influences the sharing component of P2P communities. Users who share do so to attempt "to reduce...costs" as made clear by Cunningham, Alexander and Adilov. [39] In their work Peer-to-peer file sharing communities, they explain that "the act of sharing is costly since any download from a sharer implies that the sharer is sacrificing bandwidth". [39] As sharing represents the basis of P2P communities, such as Napster, and without it "the network collapses", users share despite its costs in order to attempt to lower their own costs, particularly those associated with searching, and with the congestion of internet servers. [39]

User motivation and size of community

User motivation and the size of the P2P community contribute to its sustainability and activity. In her work Motivating Participation in Peer to Peer Communities, Vassileva studies these two aspects through an experiment carried out in the University of Saskatchewan (Canada), where a P2P application (COMUTELLA) was created and distributed among students. In her view, motivation is "a crucial factor" in encouraging users to participate in an online P2P community, particularly because the "lack of a critical mass of active users" in the form of a community will not allow for a P2P sharing to function properly. [40]

Usefulness is a valued aspect by users when joining a P2P community. The specific P2P system must be perceived as "useful" by the user and must be able to fulfil his or her needs and pursue his or her interests. Consequently, the "size of the community of users defines the level of usefulness" and "the value of the system determines the number of users". [40] This two way process is defined by Vassileva as a feedback loop, and has allowed for the birth of file-sharing systems like Napster and KaZaA. However, in her research Vassileva has also found that "incentives are needed for the users in the beginning", particularly for motivating and getting users into the habit of staying online. [40] This can be done, for example, by providing the system with a wide amount of resources or by having an experienced user provide assistance to a less experienced one.

User classification

Users participating in P2P systems can be classified in different ways. According to Vassileva, users can be classified depending on their participation in the P2P system. There are five types of users to be found: users who create services, users who allow services, users who facilitate search, users who allow communication, users who are uncooperative and free ride. [40]

In the first instance, the user creates new resources or services and offers them to the community. In the second, the user provides the community with disk space "to store files for downloads" or with "computing resources" to facilitate a service provided by another users. [40] In the third, the user provides a list of relationships to help other users find specific files or services. In the fourth, the user participates actively in the "protocol of the network", contributing to keeping the network together. In the last situation, the user does not contribute to the network, downloads what he or she needs but goes immediately offline once the service is not needed anymore, thus free-riding on the network and community resources. [40]


Corporations continue to combat the use of the internet as a tool to illegally copy and share various files, especially that of copyrighted music. The Recording Industry Association of America (RIAA) has been active in leading campaigns against infringers. Lawsuits have been launched against individuals as well as programs such as Napster in order to "protect" copyright owners. [41] One of the most recent efforts of the RIAA has been to implant decoy users to monitor the use of copyrighted material from a firsthand perspective. [42]


In early June 2002, Researcher Nathaniel Good at HP Labs demonstrated that user interface design issues could contribute to users inadvertently sharing personal and confidential information over P2P networks. [43] [44] [45]

In 2003, Congressional hearings before the House Committee of Government Reform (Overexposed: The Threats to Privacy & Security on File Sharing Networks) [46] and the Senate Judiciary Committee (The Dark Side of a Bright Idea: Could Personal and National Security Risks Compromise the Potential of P2P File-Sharing Networks?) [47] were convened to address and discuss the issue of inadvertent sharing on peer-to-peer networks and its consequences to consumer and national security.

Researchers have examined potential security risks including the release of personal information, bundled spyware, and viruses downloaded from the network. [48] [49] Some proprietary file sharing clients have been known to bundle malware, though open source programs typically have not. Some open source file sharing packages have even provided integrated anti-virus scanning. [50]

Since approximately 2004 the threat of identity theft had become more prevalent, and in July 2008 there was another inadvertent revealing of vast amounts of personal information through P2P sites. The "names, dates of birth, and Social Security numbers of about 2,000 of (an investment) firm's clients" were exposed, "including [those of] Supreme Court Justice Stephen Breyer." [51] A drastic increase in inadvertent P2P file sharing of personal and sensitive information became evident in 2009 at the beginning of President Obama's administration when the blueprints to the helicopter Marine One were made available to the public through a breach in security via a P2P file sharing site. Access to this information has the potential of being detrimental to US security. [51] Furthermore, shortly before this security breach, the Today show had reported that more than 150,000 tax returns, 25,800 student loan applications and 626,000 credit reports had been inadvertently made available through file sharing. [51]

The United States government then attempted to make users more aware of the potential risks involved with P2P file sharing programs [52] through legislation such as H.R. 1319, the Informed P2P User Act, in 2009. [53] According to this act, it would be mandatory for individuals to be aware of the risks associated with peer-to-peer file sharing before purchasing software with informed consent of the user required prior to use of such programs. In addition, the act would allow users to block and remove P2P file sharing software from their computers at any time, [54] with the Federal Trade Commission enforcing regulations. US-CERT also warns of the potential risks. [55]

Nevertheless, in 2010, researchers discovered thousands of documents containing sensitive patient information on popular peer-to-peer (P2P) networks, including insurance details, personally identifying information, physician names and diagnosis codes on more than 28,000 individuals. Many of the documents contained sensitive patient communications, treatment data, medical diagnoses and psychiatric evaluations. [56]

The act of file sharing is not illegal per se and peer-to-peer networks are also used for legitimate purposes. The legal issues in file sharing involve violating the laws of copyrighted material. Most discussions about the legality of file sharing are implied to be about solely copyright material. Many countries have fair use exceptions that permit limited use of copyrighted material without acquiring permission from the rights holders. Such documents include commentary, news reporting, research and scholarship. Copyright laws are territorial- they do not extend beyond the territory of a specific state unless that state is a party to an international agreement. Most countries today are parties to at least one such agreement.

In the area of privacy, recent court rulings seem to indicate that there can be no expectation of privacy in data exposed over peer-to-peer file-sharing networks. In a 39-page ruling released November 8, 2013, US District Court Judge Christina Reiss denied the motion to suppress evidence gathered by authorities without a search warrant through an automated peer-to-peer search tool. [57]

See also

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Streaming media is multimedia that is constantly received by and presented to an end-user while being delivered by a provider. The verb "to stream" refers to the process of delivering or obtaining media in this manner; the term refers to the delivery method of the medium, rather than the medium itself, and is an alternative to file downloading, a process in which the end-user obtains the entire file for the content before watching or listening to it.

Grokster Ltd. was a privately owned software company based in Nevis, West Indies that created the Grokster peer-to-peer file-sharing client in 2001 that used the FastTrack protocol. Grokster Ltd. was rendered extinct in late 2005 by the United States Supreme Court's decision in MGM Studios, Inc. v. Grokster, Ltd. The court ruled against Grokster's peer-to-peer file sharing program for computers running the Microsoft Windows operating system, effectively forcing the company to cease operations.

MediaDefender, Inc. was a company that fought copyright infringement that offered services designed to prevent alleged copyright infringement using peer-to-peer distribution. They used unusual tactics such as flooding peer-to-peer networks with decoy files that tie up users' computers and bandwidth. MediaDefender was based in Los Angeles, California in the United States. As of March 2007, the company had approximately 60 employees and used 2,000 servers hosted in California with contracts for 9 Gbit/s of bandwidth.

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The eDonkey Network is a decentralized, mostly server-based, peer-to-peer file sharing network created in 2000 by US developers Jed McCaleb and Sam Yagan that is best suited to share big files among users, and to provide long term availability of files. Like most sharing networks, it is decentralized, as there is not any central hub for the network; also, files are not stored on a central server but are exchanged directly between users based on the peer-to-peer principle.


TorrentSpy was a popular BitTorrent indexing website. It provided .torrent files, which enabled users to exchange data between one another. is a website that was once produced unique original file sharing news stories, shared aggregated technology news stories from the world wide web, and had a vibrant community interaction in its user forum.

This is a timeline of events in the history of networked file sharing.

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isoHunt was an online torrent files index and repository, where visitors could browse, search, download or upload torrents of various digital content of mostly entertainment nature. The website was taken down in October 2013 as a result of a legal action from the MPAA; by the end of October 2013 however, two sites with content presumably mirrored from were reported in media. One of them— became a de facto replacement of the original site. It is not associated in any way with the old staff or owners of the site, and is to be understood as a separate continuation.

Arts and media industry trade groups, such as the International Federation of the Phonographic Industry (IFPI) and Motion Picture Association of America (MPAA), strongly oppose and attempt to prevent copyright infringement through file sharing. The organizations particularly target the distribution of files via the Internet using peer-to-peer software. Efforts by trade groups to curb such infringement have been unsuccessful with chronic, widespread and rampant infringement continuing largely unabated.

<i>TorrentFreak</i> Blog on file sharing, copyright infringement, and digital rights

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<i>Metallica v. Napster, Inc.</i>

Metallica, et al. v. Napster, Inc. was a 2000 U.S. District Court for the Northern District of California case that focused on copyright infringement, racketeering, and unlawful use of digital audio interface devices. Metallica vs. Napster, Inc. was the first case that involved an artist suing a peer-to-peer file sharing ("P2P") software company.


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