Copyright infringement is bad because it involves stealing someone's work and presenting it as one's own. Copyright infringement is an illegal activity that is punishable by law.
Downloading movies and music from the Internet is a typical example of copyright infringement, as reported by Plagiarism Analyzer, a software blog dedicated to fighting online piracy. Sharing and distributing pirated copies of music and movies has become a thriving business despite copyright infringement laws.
Another typical example of copyright infringement is plagiarizing written words. High school and university students are expelled if they are found guilty of plagiarized reports and papers. Students need to cite scholarly work as they have no right to present it as their own.