Computer software can be secured so that it only operates on a customer system that has a protection file that is unique to the system. The software is inoperable when copied to other systems, even though the protection file is copied as well. The protection file is sufficiently encoded so that attempts to alter the file for use on another system will be futile. The process of encoding the protection file is sufficiently complex, so that attempts to reverse engineer the construction of the file will also be futile. The logic that encodes the protection file is never available for direct use on the customer system. For software that is distributed on copyable media, the protection file is created by a program on the product distributor's system. When the protection file is prepared during a software download request, multiple programs are used. These programs are encrypted within a composite file. The keys for decrypting these programs are passed as a parameter to a product installation program at the conclusion of the download process. All significant programs associated with the preparation of a protection file on the customer's system are eliminated after the file is created.