A digital data computing method and system (10) for transforming an original set of computer instructions (101) into a process that makes a client program (105) and a server program (107) wherein the process operates normally only if it receives at least asynchronous replies to its requests. The server program (107) is external to the process and secured against unauthorized use, access, copying and functional analysis. Moreover, the execution speed of the process is not affected by expected time delays of the modes for communication. Further, the method and system (10) provide such that it is computationally hard to determine the response, or to determine the action the process will take after receiving a response. The method and system (10) are suitable for controlling access to computer programs for purposes such as enforcing lease agreements, licensing agreements, and the like, including time-sensitive computer programs where execution timing is critical.