Security is considered one of the crucial issues for the widespread adoption of cloud computing. Despite all research done in preventive security for cloud computing;
the high complexity and the interdependence of many software layers and infrastructures mean that in practice there are always chances for something going wrong. For this reason;
there is a need to complement preventive security measures with reactive measures. Among these;
monitoring is the most relevant approach. In this paper;
we introduce a new and robust architecture for dynamic security monitoring and enforcement specially designed for cloud computing scenarios. Our solution is therefore a complete one including a three-layered architecture;
a new language for expressing monitoring rules and a strategy based on the generation of a finite-state machine to improve the performance of the monitoring engine. © 2012 The Author. Published by Oxford University Press on behalf of The British Computer Society. All rights reserved;