File sharing is the act of circulating, facilitating or bestowing access to computer files on the Internet. File sharing does not refer to a specific technique or technology for sharing files, but is an umbrella term which encompasses a range of methods. File sharing has remained dependent upon the technology of it's day: when the Internet was blooming in the 1980's, the location (address) of files would be published on Usenet or bulletin boards. Due to the download/upload speed of Internet access, users would typically share pictures or text files. The launch of peer-to-peer programs (1999) popularised the sharing of audio files, and typically copyrighted audio files.
While file sharing is a perfectly legal act - when permission of the owner of the material is granted - it is often used to share copyrighted material without the permission of the owner of the material. Therefore, file sharing has brought about a negative reaction from some music artists (Metallica and Dr. Dre were the first artists to issue lawsuits against peer-to-peer networks) and record labels. File sharing is still (2014) one of the most popular uses of the Internet, and although economic studies have highlighted it's impact upon music and movies sales, the music and movie industries have been unsuccessful in curtailing the activity of sharing copyrighted material.
Files have been shared on the Internet (TCP/IP networks) since the 1970's; using network protocols like FTP (file sharing protocol). However, no standalone application was developed to specifically allow users to exchange files until the 1990's. The genesis of file sharing can be linked to the creation of MP3. MP3 is an audio data compression technology which reduces the size of music/audio files. MP3 was standardised in 1990/1991 and was released in 1995. Software applications - named media/mp3 players - were developed from 1996-1998: which were capable of "ripping" audio files from CD's and creating an MP3 file in the process. MP3 was a phenomenon, in part, due to the fact that the majority of Internet users were dialup Internet users. MP3 enabled users to download music files - which they were incapable of doing within an acceptable timeframe - for the first time.
To satisfy and sate the appetite of users looking for MP3 files to download, file sharing (peer-to-peer) programs were created. File sharing came to worldwide prominence with the release of Napster in 1999. Napster was created by Shawn Parker and is credited as being the first peer-to-peer file sharing program. Napster allowed people to share files over the Internet; although it primarily shared audio files encoded in the MP3 format. Napster "ran into" legal issues - due to it operating a centralised database of download locations - and was deemed to have engaged in copyright infringement, and was shutdown in 2001.
However, the end of Napster was not the end of file sharing: a game of "cat and mouse" was begun, with new file sharing programs being created that attempted to circumvent copyright infringement. While file sharing programs, like Audiogalaxy and Kazaa, were successful in the short term, their fate was the same as Napster's eventually. However, while Napster only allowed users to download/upload/share a selection of file types; with subsequent programs (client programs referred to as client-side programs) allowed users to exchange a wider variety of file types.
The technology behind file sharing varies from program to program, and network to network. To circumvent copyright laws, file sharing networks have devised various structures in which users can share files. BitTorrent - and Torrent files - is a relatively new file sharing technology. Torrents use metafiles to link to content: making the direct link between file downloaders and uploaders less obvious. Websites which publish metafiles, like Pirate Bay, have come under fierce legal scrutiny and legal challenges to shut the website down. Therefore, file sharing programs have had to continually alter/update their service so as to not "fall foul" to legal challenges.
One of the "chief" problems that users have experienced with file sharing programs is adware/spyware. Some of the most notable file sharing companies have secretly installed adware/spyware programs; typically when the said file sharing program was installed. Viruses have been another problem: with early versions of file sharing programs not including a function to scan files for viruses before they were downloaded. The developers of file sharing programs took note: most eventually promised they were adware/spyware free, and included a function to scan downloaded files for viruses.
The most controversial aspect of file sharing is piracy (and warez communities) (many software applications use keys to combat piracy). There has been a crackdown on illegal file sharing by media bodies such as the 'Recording Industry Association of America'. The RIAA have correctly cited that downloading and uploading copyrighted materials, without permission, violates international copyright infringement laws. Many users, especially in the US, have been taken to court, or, have settled out of court for fines of over $2000.
Due to the illegality of facilitating the transfer of copyrighted material, many file sharing programs/networks have been shutdown due to lawsuits and legal challenges. Napster, for example, in 2001, was ordered to stop the trading of copyrighted material. Similar scenario's have effected: eDonkey, LimeWire, Grokster, and the Madster network. LimeWire, for example, in 2010, was ruled to have committed copyright infringement in a United States District Court.
It should be highlighted that file sharing / peer to peer sharing programs have a perfectly legal use. Sharing files which are not copyrighted is legal, it is only when copyrighted files are uploaded and downloaded - without the express permission of the owner - that the use of such programs becomes illegal.