  Virtualization technologies allow multiple tenants to share physical
resources with a degree of security and isolation that cannot be guaranteed by
mere containerization. Further, virtualization allows protected transparent
introspection of Virtual Machine activity and content, thus supporting
additional control and monitoring. These features provide an explanation,
although partial, of why virtualization has been an enabler for the flourishing
of cloud services. Nevertheless, security and privacy issues are still present
in virtualization technology and hence in Cloud platforms. As an example, even
hardware virtualization protection/isolation is far from being perfect and
uncircumventable, as recently discovered vulnerabilities show. The objective of
this paper is to shed light on current virtualization technology and its
evolution from the point of view of security, having as an objective its
applications to the Cloud setting.
