The present invention provides a system for creating an application software environment without changing an operating system of a client computer, the system comprising an operating system abstraction and protection layer, wherein said abstraction and protection layer is interposed between a running software application and said operating system, whereby a virtual environment in which an application may run is provided and application level interactions are substantially removed. Preferably, any changes directly to the operating system are selectively made within the context of the running application and the abstraction and protection layer dynamically changes the virtual environment according to administrative settings. Additionally, in certain embodiments, the system continually monitors the use of shared system resources and acts as a service to apply and remove changes to system components. The present thus invention defines an "Operating System Guard." These components cover the protection semantics required by .DLLs and other shared library code as well as system device drivers, fonts, registries and other configuration items, files, and environment variables.