if this option is set to yes, guests can not send a message. that is right, but they can send private messages.
if you open domain/index.php?option=com_kide&view=kide as a guest, you can click on a logged user an send private messages. it must be a bug - please fix this in consideration of security
regards
zomtec
edit:
i have to correct myself

it is possible to open private-box, but it is not possible to send as guest. i tested. you can close this thread