Any good, though not necessarily experienced, programmer will know their own level of incompetance. I've been programming for a long time, but I know I'm dangerous when I'm writing production code in a new area I'm inexperienced in. I'm especially dangerous if I don't have any emotion of fear since I think I'm doing fine even though I'm probably heading for the abyss. As others have mentioned, design/code reviews are a must to keep me honest.

Security is like error checking, you must build it into the design from the start and the quality/quantity of it must be in direct proportion to the damage that can be caused if you don't get it right. If it's some silly little app you are running on your machine from home, who cares if it gets hacked. If you are taking a CC number think "testify", "jail time", "bankruptcy" (esp. if it happens to be mine :-).

bluto