A method for avoiding the possibility of corruption when updating vital code such as boot code stored in nonvolatile memory of a unit, such as a host bus adapter, or adapter circuitry integrated onto a motherboard, or a computer system, is disclosed. Prior to updating the vital code, the method determines if the attempted update is unnecessary or regressive by reading and comparing the region version number in nonvolatile memory to the version number in the update code. If the update is unnecessary, the user is alerted. In addition, the method tests the ability to update/write to the nonvolatile memory by performing a write test operation to a less vital region prior to updating the vital region. The less vital region may comprise a test region set aside in the nonvolatile memory for performing write tests, or it may be an application region reserved for storing application programs.