A computer system includes various security measures to insure that semi-permanent operating programs, such a boot blocks and firmware, are updated properly. For example, the system may include a security switch that can enable a host computer to load a replacement program into another computer, such as an appliance server for example, if the other computer fails. Also, if a replacement program is being loaded over a network connection that fails, the loading can resume automatically after re-establishment of the network connection. In addition, certain programs, such as boot blocks, may be verified in an execution memory, such as RAM, and loaded into a more permanent storage memory, such as ROM, only if verified.