note moritz To put your question in different terms: How do I detect plagiarism, even if it's done by me? ;-) <p>There's a paper on that topic [http://theory.stanford.edu/~aiken/publications/papers/sigmod03.pdf|here], it's about a program called [http://theory.stanford.edu/~aiken/moss/|moss]. <p>There are other [http://www.redhillconsulting.com.au/products/simian/|code similarity analyzers] out there, it's surely worth a look. <p>If you want to detect blatant copy & paste a simple similarity search should be enough, for anything more elaborate you need a parse tree or an AST on which you can perform similarity checks. <p>There's much research done on that topic, you should fine some useful papers and implementations with your favorite search engine ;-) 667084 667084