WinDefender provides you with a service to keep your valuable files encrypted on your hard drive. When you want to use them you enter the password and then WinDefender will automatically (on-the-fly) decrypt them when reading from the hard drive (floppies, cd-rom, etc.) and encrypt them when writing to. This will occur absolutely transparently for you - WinDefender uses a special low-level driver which can work fine with any file.