Thanks to all who responded!
I dashed off my question without enough details.
Although I was thinking about hiding a password response, my actual
problem is to keep a Social Security Number from echoing on the
screen when a user enters it from the keyboard or a barcode scanner.
Thus this solution must be within a program, not within a command
file or UDC.  However, all the discussion is providing ideas for how to
handle other security problems, so it is very useful

For my present problem, I've used the FCONTROL options that many
suggested.  Since I'm writing in Transact, that's very simple.  Now the
program is all changed, and the people who got upset at seeing their
Social Security Number on the screen should be happy.

Thanks again!

Cecile Chi