Forum OpenACS Q&A: How do I ban a user from the directory package

I got a guy on my site doing job advertisements (http://community.freepascal.org:10000/bboards/message?message_id=235778&forum_id=24094). This triggered some alarm bells in me, as any registered user can access the directory package and capture a lot of e-mail addresses. It looks like false alarm after all, but I would like to ask, what is the best way to ban a not 100% trusted user from the directory package.