Abstract: This invention describes a block-by-block software updating process for mobile devices using modifications to a memory structure and a start-up process of the mobile device, that are necessary to allow a fail-safe and secure update of the device software. The memory of the mobile device is modified to store a software block currently updated during the software-update, but not overwriting an original block with an updated block before the updated block is verified. This prevents software from entering an unrecoverable inconsistent and nonfunctional state in case of a power loss or a similar problem. Furthermore, the memory modification allows altering a checksum procedure of the mobile device software to prevent any unauthorized modifications of the mobile device software.