Abstract: This invention discloses a method for preventing BIOS from viruses. It mainly uses the necessary signal produced when flash memory is written to generate a system management interrupt (SMI). Therefore, when a writing action occurs to BIOS stored in a flash memory, an SMI handler routine of BIOS can avoid the invasion of viruses. First, the necessary signal obtained from the BIOS flash memory is sent to the input pins of an SMI event source on a computer chipset so that the chipset can generate a corresponding SMI# to the computer CPU. Thus, when CPU receives the SMI#, it will check whether the BIOS flash memory is being written through the SMI handler routine of BIOS. If it is verified to be the viruses invasion, then the writing action is forbidden.