When we request travel/accommodation support for fudcon we normally
communicate via tickets and it get updated to fudcon-planning list. 
Most of the time for those who require supporting documents for VISA put
their personal details as entire communication is over the ticket
(inlcuding flight details).
But these information available to public. For example, someone can easily
find my previous sitive postal address, passport number, etc. I think we
need to find a better communication method instead of ticket itself to
communicate this kind of sensitive information.