Insider threats pose serious security concerns, some of which were highlighted with the recent Snowden revelations. This book looks at the security risks associated with an insider threat in cloud computing. Specifically, it looks into the critical challenge of assuring data confidentiality and integrity for the execution of arbitrary software in a consumer's virtual machine. The problem arises from having multiple virtual machines sharing hardware resources in the same physical host, while an administrator is granted elevated privileges over such host. The research presented in this book includes, the results of an empirical approach to collect evidence of the existence of security problems linked with an insider threat, and the implementation of a novel prevention mechanism for such a problem. Finally, this research work concludes with a proposal for a trustworthy cloud architecture that uses the security properties our prevention mechanism guarantees as a building block.