Remove UIAlertview from window | background

for (UIWindow *v in [[UIApplication sharedApplication] windows]) {
      NSLog(@"Window Description : %@",v.description);
      for (UIView *vv in [v subviews]) {
          if([[vv description] hasPrefix:@"<UIAlert"] == YES){
               UIAlertView *al = (UIAlertView *) vv;
               [al dismissWithClickedButtonIndex:0 animated:NO];
            }
      }
}