Cloud computing is a new paradigm providing software and hardware resources according to the customers' needs. However, it introduces new security risks such as confidentiality of data stored in cloud databases. Actually, this last risk is a crucial issue that must be addressed as ciphering mechanisms are not sufficient to guarantee a strong confidentiality of data. In this paper, we discuss the main cloud computing security risks and focus on the data confidentiality problem in the context of e-commerce clouds. We describe the design of a data concealment component that we propose to resolve this problem. Evaluating this component, we find that it successfully conceal data of legitimate users and protect them against potential attacks.