The concept of legal professional privilege (LPP) in the Common Law is to enable a client to make full disclosure to his legal advisor for seeking advice without worrying that anything so disclosed will be used against him. Thus, some of the communications and documents between a legal advisor and his client can be excluded as evidence for prosecution. Protection of LPP information in the physical world is well addressed and proper procedures for handling LPP documents have been established. However, there does not exist a forensically sound procedure for protecting digital LPP information. In this correspondence, motivated by a real case of a commercial crime investigation, we introduce the LPP data integrity problem. While finding an ideal solution to solve the problem is difficult, we propose a practical solution that was adopted to solve the real case investigation. We also analyze the performance of our solution based on simulated data.