After a year of legal battles with the music industry, the controversial file-sharing service Napster has finally been forced to block access to copyrighted songs.

Napster is a free program and Internet service that allows its users to easily search for and download CD-quality music from another Napster user’s computer. However, the music industry maintains that Napster is nothing more than a haven for mass piracy, since a great majority of the songs traded by Napster users are copyrighted works.

The Recording Industry Association of America, a trade group that represents the world’s five largest record labels, filed suit against Napster in December of 1999 because artists and record labels collect no royalties from downloaded songs.

Napster has argued that its service, much like radio, acts as a promotional tool. Users can useNapster to sample an album before making a decision to purchase it. However, the major record labels maintain that Napster users do not buy CDs after they have downloaded the songs they want.

Napster also argued that it had a number of legitimate applications such as distributing the works of lesser-known artists and legal live recordings that are never released on CD.

Despite Napster’s arguments, U.S. District Court Judge Marilyn Hall Patel ruled last July that Napster must prevent its users from trading copyrighted songs. Napster challenged the injunction in the Court of Appeals less than two days later stating that the injunction would effectively shut the service down permanently despite its legitimate applications.

The Court of Appeals ruled that Patel’s original injunction was too harsh and ordered that the injunction be rewritten.

The new injunction, issued on March 5, asks Napster and the music industry to share the burden of policing Napster’s system. If a record label wants a song banned from being traded on Napster, it must provide Napster with the song title, artist name, a file name for a traded song, and certification of copyright.

Upon receiving this information, Napster has three business days to ban the song from its search database.

Napster blocks access to these copyrighted works by using a two-tiered filtering system. The first filter breaks the file name into individual words. If the filter finds the name of an artist, it compares the file against the song title database. If there is a match, the file is blocked from Napster’s system. If the file passes the first filter, the file is compared to the filename submitted by the record labels.

On behalf of the five major record labels — Sony, Warner, BMG, EMI and Universal – the RIAA submitted a list of 135,000 songs to be blocked from Napster’s database late last Friday. Napster had until Wednesday to block the songs.

Napster ran into complications when more than 46,000 of the songs submitted by Sony failed to provide file names with the artist names and song titles. Those songs have not been blocked from Napster’s system.

“Most of the names were in conjunction, but 50 percent of Sony’s list did not have file names and that’s a clear violation of the injunction,” said Hank Barry, Napster CEO. “We’re not asking for them to provide us with every file name for every work on the system. We just want one.”

Napster has also run into problems with the filtering process itself. Users are finding many ways to modify the file names of songs in order to avoid being caught by the filters.

One popular way to evade the filtering process is to replace certain words with numbers. For example, the anti-Napster heavy metal group Metallica, which is currently involved in its own lawsuit against Napster, wrote the songs “Unforgiven” and “Fade to Black.” Napster users have bypassed the filtering system by renaming the files “Un4given” and “Fade 2 Black.”

Also, Canadian firm PulseNewMedia was quick to release software that renames files in a way similar to pig latin. It moves the first letter of each word to the end of the word. For example, Metallica would become “etallicaM.”

“Nobody expects us to get all the variants within three business days,” said Barry. However, he stated that the company is working on an advanced filtering system that he believes “will pick up 99 percent of the variants.”

Although it would be easier to just block all works by a particular artist, it would also block things such as live recordings of The Grateful Dead that the band has allowed its fans to trade.

Napster plans to roll out a subscription-based service with Bertelsmann AG, which owns BMG, this summer. The proposed Napster service will charge its users a flat monthly fee for unlimited access to songs. The money would then be distributed to copyright owners in proportion to the downloads.

Napster hopes to strike a deal with the other major labels in order to legally license their works for the new Napster service. However, all attempts, including an offer to pay the labels $1 billion over the next five years, have been rejected.