The User Defined Fields Tab is the tab on the License Project Properties dialog where you can define a set of string, date a numeric values to be manipulated at run time through the ClientProtector interface.  These field values are stored inside the encrypted license and so are just as secure as the license data itself.

The tab looks like this:

Strings may be of any length and can be stored in any of ten fields.  

Dates may be any Gregorian date after December 30, 1899 (the default).

Numeric values are signed 32-bit integers.

Any of these fields can be set and retrieved using the ClientProtector interface at run-time.  

Note that in general these fields are not used by the ClientProtector logic (generally, see below) and are for your discretionary use for storing secure data. Note also that you can use the numeric and date fields as parameter values when activating a Design-Time Composite Authorization Definition.