A portable rewritable medium and a method are provided for preventing unauthorized use of executable software stored on the portable rewritable medium. A portion of the software stored on the portable rewritable medium may include instructions for a processing device to determine whether execution of the executable software is permitted. If execution of the executable software is permitted, the processing device may execute the executable software directly from the portable rewritable medium. Characteristics of the portable rewritable medium may be checked to determine whether functionality of the executable software is to be limited.