A data storage device including a non-volatile memory and a micro-controller is provided. The non-volatile memory includes a first block and a second block, wherein the first block stores firmware code. The micro-controller writes one predetermined string into the second block before an execution of the firmware code, and determines whether there is more than one predetermined string in the second block. In response to there being no more than one predetermined string in the second block, the micro-controller allows the execution of the firmware code and erases the predetermined string in the second block upon successful completion of a prerequisite procedure during the execution of the firmware code. In response to there being more than one predetermined string in the second block, the micro-controller does not allow the execution of the firmware code.