The federation of clouds can provide benefits for cloud-based applications. Different clouds have different advantages – one might be more reliable whilst another might be more secure or less expensive. However, being able to select the best combination of clouds to meet the application requirements is not trivial.This paper presents a novel algorithm to deploy workflow applications on federated clouds. Firstly, we introduce an entropy-based method to quantify the most reliable workflow deployments. Secondly, we apply an extension of the BellLaPadula Multi-Level security model to meet application security requirements. Finally, we optimise deployment in terms of its entropy and also its monetary cost, taking into account the price of computing power, data storage and inter-cloud communication.To evaluate the new algorithm we compared it against two existing scheduling algorithms: Dynamic Constraint Algorithm (DCA) and Biobjective dynamic level scheduling (BDLS). We show that our algorithm can find deployments that are of equivalent reliability but are less expensive and also meet security requirements. We have validated our solution using workflows implemented in the e-Science Central cloud-based data analysis system