 This is the distinguishing factor between plagiarism, which is not a crime, and copyright infringement, which may be a cause of legal action from the author.The most fundamental form of attribution is the statement of the copyright holder's identity, often in the form "Copyright © [year] [copyright holder’s name]".The preservation of such a notice was an invariable requirement to prevent a work entering the public domain; this changed in the United States on March 1, 1989 when the requirement of copyright registration and copyright signment was ended.