Attorneys that represent major music and movie companies are asking the US Supreme Court to review a federal court ruling which stated that decentralized file-sharing networks like Grokster were not responsible for copyright infringement.
In the Grokster case, the judges ruled that individual users were responsible for what was shared on such networks. The Ninth Circuit Court of Appeals said suing Grokster is like suing VCR makers when VCRs have legitimate purposes.
With the Grokster ruling in mind, groups like the RIAA have sued over 5,000 individuals for file-sharing copyrighted material. Despite this effort, studies show that more people are doing this. Thus, the RIAA and MPAA want to go after companies. Source