post message to user's wall but disallow user's friends from seeing that message

I am creating an iPhone app using FBConnect. I can easily post a message to a user's wall.

My problem is that this message can be seen by all the user's friends (normally). I want to disable this; I 开发者_如何学Gowant it so that the user's friends cannot see that message.

How can this be done?

NSString *feedpath = [NSString stringWithFormat:@"%@/feed",idFriend];
    //NSLog(@"fappDelegate.facebooklogin.facebook is%@",appDelegate.facebooklogin.facebook);

    [appDelegate.facebooklogin.facebook requestWithGraphPath:feedpath 
                                                   andParams:[NSMutableDictionary dictionaryWithObject:@"I am in iphone app" forKey:@"message"]
                                               andHttpMethod:@"POST"
                                                 andDelegate:self];

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I think the owner of the facebook account sets the settings for his privacy policy, and those settings dictate who can see his wall messages.

See facebook privacy settings, point 9.