A method for protecting data, adapted for a computer system, is provided. The computer system includes a storage device. The method includes: when the computer system executes a power-off procedure, inspecting whether a preset external storage device is connected to the computer system; if it is determined that the preset external storage device is connected to the computer system, when the computer system executes the power-off procedure, backing up data of a predetermined segment of the storage device to the preset external storage device, and generating a back-up data, and then writing a specific data template to the predetermined segment for covering original data of the predetermined segment.