You should add the ability possibility to create private tickets. If you read the other ticket about categories, I can explain you what I mean exactly:
I saw this feature at phpbb. You can create private tickets, which are only visible to staff members. Only staff members and the creator can see the ticket in the private tickets category. Could be very useful if you found a security issue like an exploit or something else.
Private Tickets is a good idea, but there is no need for categories, thats basically what Components are for. I might put a check box on the New Ticket page to toggle if it's private or not.