Abstract: A security box is provided with a closure inserted or removed from a channelled opening in one wall thereof. The closure has a security plate attached to the inside wall thereof, which security plate has rearwardly extending flanges on two sides thereof with a portion between said sides having a flange with an elongate tongue portion adapted to extend through a slot in the channel in the box such that a latch bar of a lock can nest in an opening in the tongue behind the channel for locking the closure in place on the box. The other end portion of the security plate has an offset ledge spaced from the wall of the closure such that the ledge is positioned behind one edge of the opening in the box which, in combination with the lock, prevents removal of the closure from the box.