Recording industry lawyers have claimed that detailed analysis of the data in MP3 music files can prove the files were downloaded illegally from an online file-sharing network.
The revelation came with the release of court documents relating to a case against a New York woman. She is accused of sharing 1000 songs through a peer-to-peer file network, using the online pseudonym "nycfashiongirl". She claims to have made the MP3 files found on her computer from CDs that she owned.
But lawyers for the Recording Industry Association of America (RIAA), which represents the world"s largest record companies, write in a court document: "The source for nycfashiongirl"s sound recordings was not her own personal CDs."
The RIAA says the username of another computer user was found in the header of one of the MP3s. Headers are routinely used to store a song"s title and length, but some MP3 compression software may also add information such as the username of the person who created the file.
The RIAA said that it also examined the digital fingerprints, or "hashes"", of the MP3s and found that some matched those of files previously see on file-sharing networks.
Markus Kuhn, a computer researcher at Cambridge University, UK, says the process of MP3 encoding involves variables that can create tell-tale differences between two files of the same song.