Encyclopedia Britannica defines plagiarism as the act of taking the writings of another person and passing them off as one's own. If only thoughts are duplicated, expressed in different words, there is no breach of contract. Also, there is no breach if it can be proved that the duplicated wordage was arrived at independently.

Plagiarism is the act of claiming to be the author of material that someone else actually wrote. Students have plagiarized book reports, term papers, essays, projects, and graduate-degree theses. Teachers—including college professors—have plagiarized journal articles, course materials, and textbooks. Researchers have plagiarized reports, articles, and book chapters. Although academic plagiarism is not new, what is new since the latter years of the 20th century is the ease with which writings on virtually any topic can be misappropriated with little risk of detection. The principal instrument responsible for the recent rapid rise in academic plagiarism has been the Internet.

Especially popular are the on-line “paper mills” or cheat sites—companies that sell students completed essays, book reports, projects, or theses that can be submitted in school under the students' own names. At least 150 cyber paper mills have been operating over the past three years. Those available on the World Wide Web bear such names as Evil House of Cheat (more than 8,000 essays), Genius Papers, Research Assistance, Cheat Factory Essay Warehouse, School Sucks, Superior Term Papers, and 12,000 Papers.com. In Germany, <cheatweb.de> advertised high-scoring essays, term papers, stories, interpretations, book reports, and other types of homework. The site reported having between 3,000 and 5,000 high-school and college users daily.

Just as the Internet has greatly expanded students' opportunities to plagiarize, however, it has also increased teachers' ability to discover sources from which students have lifted material. This new ability to discover plagiarism is attributed to Web-plagiarism checkers or verifiers.

The typical Web checker is an Internet service that works in the following way. A student's paper is entered into the checker's Web site. That Web site is programmed to compare the contents of the paper with the contents of thousands of documents on the World Wide Web. A report showing how much of the student's paper is identical to, or highly similar to, documents on the Web is sent back to the teacher, and the report identifies what those original documents were.

Web checkers usually charge for their services, either a flat annual fee or a stated amount for each paper processed. One popular plagiarism checker is <turnitin.com>. In 2001 the operators of the site claimed 20,000 subscribers worldwide. Another much-used checker is the Essay Verification Engine (EVE), which conducted 45,840,495 assessments between February 2000 and late August 2002. Educators who have used Web-plagiarism checkers report that telling students that their papers will be Web-checked reduces the incidence of Internet plagiarism.