The field should have these attributes:
- A text field that is visible on during registration only. (I have done this with Field Type: Text Field; Allow Users to View: Yes; Viewing Settings: No to All)
- This text field acts as Confirmation code, but has one (or more) admin defined codes. This allows restriction of new members based on a code previously communicated. (should I clone and edit the captcha module?)
- Optional: If possible, storing a list of selected words in the database (along with word expiry dates) would make this feature perfect.