The difference between copyright infringement and plagiarism:
Copyright infringement is using someone else's creative work, which can include music, videos, a movie clip, a piece of visual art, a poem, a photograph, or other creative works, without permission.
Plagiarism is using someone else's work without giving proper credit or the failure to cite the work adequately.
The courts enforce copyright infringement.
Schools enforce plagiarism.
Peer-to-peer applications and file sharing have become widespread, especially within the student community. Although using file-sharing software, such as KaZaA or Morpheus, is not illegal itself, distributing copyrighted material without permission is. Such activity may violate federal copyright laws.
Under the Digital Millennium Copyright Act (DMCA), the Recording Industry Association of America (RIAA) and similar organizations can and have issued subpoenas to a university when someone on that institution's network has been found to be distributing copyrighted materials. The subpoena may request the identify of the user and that can be the first step towards legal action.
Indiana University has a site worth visiting that addresses file sharing issues from a student perspective, File Sharing @ IU. It's Copyright Tutorial examines file sharing in the context of copyright.