Plagiarism is a heavy sin in education world. You can get a maximum penalty of being expelled if the staff found an evidence that you conduct this act. Many education places have created a string rules about it and it was used effectively for each assignment. I also have done the same thing for my class.
Detecting plagiarism is not an easy task as it would take a lot of efforts and time when you have so many students taking your class. For paper work, you can use Turnitin service which i think is the best plagiarism checker available for now. It's not free, but i think it's worthed, mostly if you ask for your students to create a journal which will be published.
For code plagiarism, this is even more interesting as source codes are available on the Internet and all you need is browse on search engines and you will get a bunch of codes. Stanford has created a system which can help us to detect software plagiarism called Moss (Measure Of Software Similarity) and i'm using it currently. It has been developed since 1994 and it has been updated constantly with new algorithm and mechanism.
If you want to find out about Moss, visit their website or see the background paper about this research. Moss is created by Alex Aiken
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