End of semesters often mean term papers. Here are a few source of anti-plagirism software that might make your job a tad easier.
From the University of Virginia Plagiarism Resource Site Windows Software Page
From the University of Washington
Another site that discusses many free sources for both teacher and student.
This is not to say I have had a problem lately, but it is always better to be prepared for these things.
My note to students: always give credit to those sources you use!