1. A method performed by one or more computers to track virtual machine images (VMIs) deployed on hosts, respectively, the method comprising: automatically maintaining linking information that links application elements to the hosts, the linking information comprising element linkage information indicating which of the application elements were used to build or compile which of the applications, the linking information further comprising application linkage information indicating which of the applications are installed on which of the VMIs, the linking information further comprising VMI linkage information indicating which of the VMIs reside on which of the hosts, the application elements comprising source code files not present on the VMIs, wherein the applications comprise binary executable files executable within the VMIs, and wherein the VMIs are executed as virtual machines by hypervisors on the hosts, respectively; and responding to queries identifying respective source code files by, for a given query for a given source code file, accessing the linking information, using the element linkage information to identify any of the applications that were used to build or compile the given source code file, using the application linkage information to identify any of the VMIs having any of the identified applications installed thereon, and by using the VMI linkage information to identify any of the hosts hosting any of the identified VMIs, wherein a reply to the given query comprises indicia of the identified hosts.