Software security refers to whether or not users will have difficulty running the software after the turn of the century because of keycode related issues.
Internal dates refers to how dates are stored and used within the applications itself.
This means that permanent licenses do not have a time out date, and the software will continue to run into the next century without interruption. The other consideration is how dates are handled internally in the software. Software vendors that use an 8-bit stamp are expected to have difficulty at the turn of the century.