Anonymous Users, Forms Pages, and the Lockdown Feature
stsadm.exe –o activatefeature –url <site collection url> -filename ViewFormPagesLockdown This will enable the lockdown feature on your site collection. If you already had anonymous access enabled, you'll need to go disable it, then enable it again. Go to the _layouts/setanon.aspx page, switch anonymous access off, click OK, then go back and set it to on, click OK. You should now get an authentication prompt when you try to navigate to a forms page http://blogs.msdn.com/b/ecm/archive/2007/05/12/anonymous-users-forms-pages-and-the-lockdown-feature.aspx