A method for validating the data defining an executable program prior to loading of the data for program execution is described. The method includes calculating a verification number for the data within a primary data storage area, the data defining an executable program, comparing the calculated verification number with a stored number, executing the program within the primary data storage area if the verification number matches the stored number, calculating a verification number for the data within a secondary data storage area, the data within the secondary data storage area defining the same executable program as that within the primary data storage area, if the verification number and the stored number do not match, comparing the calculated verification number for the data within the secondary data storage area with the stored number, causing the program to be executed if the verification number for the data within the secondary data storage area and the stored number match, and indicating a failure if the verification number for the data within the secondary data storage area and stored number do not match.