1. A computer-implemented method comprising: receiving, by one or more computing systems of a virtual machine image importation service and from a client of the virtual machine image importation service, a virtual machine image with at least one installed operating system; retrieving, by the one or more computing systems, a plurality of defined identification vectors that are each associated with one or more of a plurality of known operating systems; applying, by the one or more computing systems, one or more heuristic assessment tests to the virtual machine image to identify the at least one installed operating system, wherein applying the one or more heuristic assessment tests includes comparing test results from the applying of the one or more heuristic assessment tests with the retrieved plurality of identification vectors; modifying, by the one or more computing systems and based at least in part on the identified at least one operating system, the virtual machine image by performing one or more modifications to one or more configuration files of the identified at least one operating system; and providing, by the one or more computing systems, access of the client to the modified virtual machine image.