Turnitin is a plagiarism detection service.  The Turnitin software checks for potentially unoriginal content by comparing submitted work to several databases using a proprietary algorithm. It scans its own databases, and also has licensing agreements with large academic proprietary databases.  All work submitted by students is stored in a database used to check for plagiarism. This prevents one student from using another student's work, by identifying matching text between papers. In addition to student work, the database contains a copy of the publicly accessible Internet, with the company using a web crawler to continually add content to Turnitin's archive. It also contains commercial and/or copyrighted pages from books, newspapers, and journals.