A file protection method of a computer apparatus including a processor, the method including extracting classes from an executable file of a package file, classifying the classes into class groups, adding a loading code to a first class group among the class groups, the loading code configured to cause sequential loading of the class groups to a memory in a random loading order in response to execution of the package file, adding an integrity code to a second class group among the class groups, the integrity code configured to verify an integrity of a corresponding class group among the class groups or a previous class group among the class groups, the previous class group including the loading code configured to cause the corresponding class group to load, and regenerating the package file using the class groups after the adding the loading code and the adding the integrity code.