In one form the invention provides a method of modifying a data file for transmission over a data network. The method comprises the steps of receiving the original data file and creating a header file, the header file including the length in bytes of the original data file. At least one repetition byte sequence is identified within the original data file, the repetition byte sequence comprising a byte value that is repeated consecutively within the repetition byte sequence. A modified data file is created by replacing the repetition byte sequence with a repetition marker, the repeated byte value, and a repeat frequency value representing the number of times the repeated byte value occurs within the repetition byte sequence. The repetition marker is added to the header file. The invention further provides a method of transmitting a data file to a remote device over a data network.