My final year project in uni was a tool to detect plagiarism by analyzing whether parts of an assignment had been outsourced to anyone else (basically did one author write the document on their own). Or if two projects by the same student were actually written by one person. For what was at the time an extremely naive implementation of various stylometric methods it worked surprisingly well. Even I was shocked when I managed to demonstrate the tool working. People should read about this branch of studies if they care at all about anonymity online.