A hex editor is a computer program that allows users to edit the binary code, represented by hexadecimal values, which makes up a computer file. Using a hex editor you can view and edit the raw file data, making modifications down to the core programming of the software application.
A number of free hex editors are available for download. Features range from simple to complex. While some provide only a raw look at the binary code, some provide a rich set of tools for interpreting and editing the data.