The Impossibility of Understanding Security

As a UX designer or someone working with front end and the look and feel maybe of an interface, it often makes the case that you'll go to the coder. And that in itself is like a black box. You almost expect them to know everything about what goes on from that point onwards. Whereas in all true of reality, they probably don't. I mean, there could be a worm in there. When I say worm, that means let's say virus, whatever. Or bug or whatever. Can you do this or not?