Ron, just as se7en said, I would probably just place a security file within the Autocad folder and give it an extension that doesn't stand out, you know like acad.mpi or ddvpls.tbl. Then incoporate your security into this file. Make it read every 5th or 6th character on until it gets all the characters it needs to fulfill the criteria needed. As everyone else has stated, your average CAD user won't have a clue what to look for.