An apparatus providing for a secure execution environment including a microprocessor and a secure non-volatile memory. The microprocessor executes non-secure application programs and a secure application program. The non-secure application programs are accessed from a system memory via a system bus. The secure application program executes in a secure execution mode. The microprocessor has secure execution mode logic that monitors conditions corresponding to the microprocessor associated with tampering, and causes the microprocessor to transition to a degraded operating mode from the secure execution mode following detection of a first one or more of the conditions. The degraded operating mode exclusively provides for execution of BIOS instructions. The secure non-volatile memory is coupled to the microprocessor via a private bus, stores the secure application program. Transactions over the private bus are isolated from the system bus and corresponding system bus resources within the microprocessor.