In our work, we came up very specific functional requirement for excel spreadsheet we maintain.
We need one of the column to have following properties:

- All cells in the column must have unique values (will use some mathematical hash function to do it, so this is not core of question here)
- Only empty cells in this column can be edited and it can be edited only once.
- Once it has value, it can not be edited at all. Not under any circumstances.

Is it possible, does it need VBA programming or can be accomplished without programming? Thanks.,

NOTHING???? No-body has clue?

Excel is not that secure, but you could try locking all but the empty cells in the column and using a password.
Then use the Worksheet_Change event to lock empties as used.