MOSS: A System for Detecting Software Plagiarism


Sample output from Fall 2009: Summary; detail 1, 2, 3, 4, 5, 6, 7.


What is Moss?

Moss (for a Measure Of Software Similarity) is an automatic system for determining the similarity of C, C++, Java, Pascal, Ada, ML, Lisp, or Scheme programs. To date, the main application of Moss has been in detecting plagiarism in programming classes. Since its development in 1994, Moss has been very effective in this role. The algorithm behind moss is a significant improvement over other cheating detection algorithms (at least, over those known to us).

An Internet Service

Moss is being provided as an Internet service. The service has been designed to be very easy to use--you supply a list of files to compare and Moss does the rest.

You can use Moss from either Unix or Windows systems. To use the Windows submission script you will need to replace the script you receive via email with the Windows version (see instructions for downloading scripts below).

In response to a query the Moss server produces HTML pages listing pairs of programs with similar code. Moss also highlights individual passages in programs that appear the same, making it easy to quickly compare the files. Finally, Moss can automatically eliminate matches to code that one expects to be shared (e.g., libraries or instructor-supplied code), thereby eliminating false positives that arise from legitimate sharing of code.

Registering for Moss

Moss is being provided in the hope that it will benefit the educational community. Moss is fast, easy to use, and free. In the past, access has been restricted to instructors and staff of programming courses. This is no longer the case, and anyone may obtain a Moss account. Moss is, however, not to be used for commercial purposes.

To obtain a Moss account, send a mail message to moss@moss.stanford.edu. The body of the message should appear exactly as follows:

registeruser
mail username@domain

where the last bit in italics is your email address.

If you already have an account, the latest submission script can be downloaded here.

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