Security issues of the combined usage of Grid and Cloud resources

The efficient use of e-Infrastructures requires researchers to combine Grid, High Performance and Cloud resources in a way that allocates rationally the physical resources among the research tasks and activities and minimizes the movement of data and the waiting times. The high complexity of the computing infrastructure available for researchers underlines the importance of clear understanding of the security treats and devoting sufficient resources for their mitigation. In Eastern Europe there is a tradition of joint operations and usage of Grid and High Performance Computing resources for the needs of research and education. In this paper we identify some important use cases of combined usage of Grid and Cloud resources and consider the security treats and attack vectors that should be the prime target for investigation and mitigation in this context. By leveraging our experience from the so-called Security challenges in the EGEE Grid infrastructure, we identify steps and best practices that could decrease the risk from penetration by random as well as determined attackers and outline services that could bring down the overall security risks.