A disk drive according to the invention has a processor for executing a program for identifying harmful computer code (HCC). A communication protocol with the host computer according to the invention provides means for the host to control the HCC detection process, receive information about the HCC detection from the disk drive and preferably for the HCC detection program to be transmitted to the disk drive. In a preferred embodiment a disk drive has a scanning program for scanning data for harmful computer code (HCC) using a set of HCC signatures. In one embodiment, the disk drive has means for communicating with a controlling host computer which implements the HCC protocol and a user computer which does not implement the HCC protocol, to allow the user computer to be protected from HCC in a transparent way.