If a not logged in user is clicking on a users avatar (In a forum) you get an 404 error page.
I´m using sociable so in the settings "Integration" I have Sociable to show a users profile.
If I change it to CJForum I only get the "You do not have permission" message which seems more correct.
If the problem can be solved why worry?
If the problem can not be solved, worrying will do you no good.