Warning users to activate their account by e-mail

[Kanustep]

Hi,

I have some users that still don't activate their account by e-mail, but they visit the site with frequency so I don't want to delete them.
However I would like to put a Warning that when they enter will show some message like:

"Please activate your account by clicking in the link on your e-mail to view the forum"

I have search for this in mod section but don't return nothing, can you tell me how to do it?

Thank you

The only way I can found is to give only access to usergroup that don't activate their account by e-mail to a forum with the message, but this can be tricky since user can think it is a error.

How do you do in your forum to that group of users?