Plagiarism has long been a problem in the academic world. Some universities subscribe to plagiarism detection services (PDSs) to determine whether students have lifted whole passages of text from other sources without attributing the content to the source. Committing plagiarism can lead to extreme discipline up to automatic failure in the course or expulsion from the school. (I know of a case in each instance.)
Not all professors believe in using PDSs. The Conference on College Composition and Communication (CCCC), a division of the National Council of Teachers of English, has established a position against its use. In Intellectual Property-Related Motion at the CCCC Business Meeting, the CCCC asserts that using a PDS creates a hostile learning environment that inhibits a writer's development and shifts the responsibility of assessing writing from teachers to technology.
We can argue these points forever, but one of the CCCC's resolutions seems fair: schools using a PDS should encourage students to submit their drafts to the service before submitting the final version to their professor. This sensible response will ensure that students are educated about the limits of intellectual property and about their ethical obligations as writers.