15. The computer-readable storage medium of claim 14 , wherein the registered code signature module is called by a routine in the operating system to verify the digital signature corresponding to the code portion to ensure that the code included in the code portion has not been modified.
15. The computer-readable storage medium of claim 14 , wherein the registered code signature module is called by a routine in the operating system to verify the digital signature corresponding to the code portion to ensure that the code included in the code portion has not been modified. 17. The computer-readable storage medium of claim 15 , further comprising computer executable instructions for performing steps comprising: the operating system generating a first hash value from the digital signature corresponding to the code portion of the application document; the operating system calling the registered code signature module to form a second hash value for the code portion of the application document and to compare the first hash value and the second hash value.