[GeorgeB85]

This would be good, but since the code is indefinitely always the same, unless the person who created the pass code changes it, it isn't fool proof.

A real person, could get the pass code, register, and then since it doesn't change. Use the same passcode to create tons of bots to spam the heck out of the forums.

This is why I love Valters Advanced Registration mod. The password changes each time a new invitation is sent out, and the pass code can only work with the email address it was sent to.

Also, if a real human did register, then send a bunch of invitations out and registered as bots, you could delete them all, and the user, as there is a log of all invitations sent out, that states who the user is that sent out the invitation.