Code clones in software increase maintenance cost and lower software quality. We have devised a new algorithm to detect duplicated parts of source code in large software. Our algorithm is adequate for large systems and detecting not only the exact but also similar parts of source code. Our simulation of this new algorithm, namely SDD (Similar Data Detection), indicates that it can detect duplicated parts of source code in huge software with high performance. Categories and Subject Descriptors D.2.13 [Software Engineering]: Reusable Software – Reuse models. General Terms: Algorithm, Experimentation Keywords Duplicated code, code clone, system maintenance, search index