a microprocessor includes a model specific register having an address , fuses manufactured with a first predetermined value , and a control register . the microprocessor initially loads the first predetermined value from fuses into the control register . the microprocessor also receives a second predetermined value into the control register from system software of a computer system comprising the microprocessor subsequent to initially loading the first predetermined value into the control register . the microprocessor prohibits access to the msr by an instruction that provides a first password generated by encrypting a function of the first predetermined value and the msr address with a secret key manufactured into the first instance of the microprocessor and enables access to the msr by an instruction that provides a second password generated by encrypting the function of the second predetermined value and the msr address with the secret key .