4.3 Unallocated Ranges

Usually a compound file will include ranges of bytes that are not allocated for either CFB structures or for user-defined data. For instance, each stream whose length is not an exact multiple of the sector size requires a trailing portion of the last sector in the stream's sector chain to be unused. Implementations that fail to initialize these byte ranges to zero (as recommended in section 2.7) might unintentionally leak user data.