Abstract: A method of protecting computer files that are pre-stored on a storage medium such as a floppy-disk, against a computer virus infection. The method includes determining a free-space value (e.g., number of bytes) not occupied on the storage medium by programs or data files. An existing file on the medium is selected and opened and a file pointer for the location of the selected file is obtained, for example, by referring to a file allocation table (FAT) on the storage medium. The value of the file pointer with respect to the location of the end of the selected file is offset by an amount corresponding to the determined free space on the storage medium, and the pointer value with the offset is re-written in the FAT. Accordingly, the free space on the storage medium becomes entirely associated with the selected file or files, leaving no apparent room on the medium for storing a computer virus.