1. A computer program product for controlling a computer to scan computer files for malware, said computer program product comprising: malware scanning code operable to malware scan all computer files stored within a storage location as addressed by an operating system to identify any computer files stored within said storage location that contain malware; identification code operable if no computer files containing malware are found in said storage location, to identify said storage location as a clean storage location; and when subsequently reading a computer file, determination code operable to determine whether or not said computer file is stored within a clean storage location and: if said computer file is stored within a clean storage location, then permitting reading of said computer file without further malware scanning; and if said computer file is not stored within a clean storage location, then malware scanning said computer file.