It's interesting that a lot of these variants were/are being created as security or tamper-proof mechanisms, a real world type of "security through obscurity" (

It's interesting that a lot of these variants were/are being created as security or tamper-proof mechanisms, a real world type of "security through obscurity" (although a different type of obscurity than is usually meant by that phrase). Then it becomes not obscure enough and they make a new type of screw.