Since assignments turned in by computer science students can be in a variety of languages, we work at the syntactic level and do not consider the source-code semantics. Consequently, the approach we propose is endogenous and makes no assumption about the programming language being analysed. It is based on an alignment method using the parallel principle at local resolution (character level) to compute similarities between documents. We tested our framework on hundreds of real source files, involving a wide array of programming languages (Java, C, Python, PHP, Haskell, bash). Our approach allowed us to discover previously undetected frauds, and to empirically evaluate its accuracy and robustness.