If defined, this directive sets the default secure delete option to on. SQLite will zero out deleted rows, as well as zero out and write back any recovered database pages before adding them to the free list. This prevents someone from recovering deleted data by examining the database file.
Be aware that SQLite cannot securely delete information from the underlying storage device. If the write operation causes the filesystem to allocate a new device-level block, the old data may still exist on the raw device. There is also a slight performance penalty associated with this directive.