Data Warehouses (DW) manage crucial enterprise information used for the decision making process which has to be protected from unauthorized accesses. However, security constraints are not properly integrated in the complete DWs' development process, being traditionally considered in the last stages. Furthermore, legacy systems need a reverse engineering process in order to accomplish re-documentation for detecting new security requirements as well as system's design recovery to enable migration and reuse. Thus, we have proposed a model driven architecture (MDA) for secure DWs which takes into account security issues from the early stages of development and provides automatic transformations between models. This paper fulfills this architecture providing an architecture-driven modernization (ADM) process focused on obtaining conceptual security models from legacy OLAP systems.