High Quality Content by WIKIPEDIA articles! FreeOTFE is an open source on-the-fly disk encryption (OTFE) computer program for PCs running Microsoft Windows, and personal digital assistants (PDAs) running Windows Mobile (use FreeOTFE4PDA). It creates virtual drives, or disks, to which anything written is automatically encrypted before being stored on a computer`s hard or USB drive. It is similar in function to other disk encryption programs including Microsoft`s BitLocker.