There are several "provably secure" computer systems. As in you can demonstrate they fulfil certain mathematical constraints and those constraints are absolute. Then you have to write the code and prove the code, then you have to hope the prover is correct and the hardwareis correct. Nothing is 100%.

As to the randomisation stuff - yes I've got examples, and we've hit the same thing in Linux with randomisation. You get cases where memory scribbles cause a problem only if the layout happens to be a specific variant (especially with stack randomisation). From "either it dies or it works" you get "1 in 10,000 times xyz app blows up". That does make debugging much much harder. Of course a good reply to that is "so improve the debugging tools".

1030. Fraud and related activity in connection with computers (a) Whoever-- (1) having knowingly accessed a computer without authorization or exceeding authorized access [...]

Determining whether or not you have authorization it the key. Does an open access point grant everyone authorization? How would you know that an open access point does NOT grant everyone authorization?

I heard a rumor about someone who was arrested for accessing an open wireless access point. The prosecution dropped the whole thing because the last question couldn't be answered. i.e. - There wasn't any warning banner saying unauthorized acccess was prohibited. I consider it a rumor since I couldn't verify the story. However, the individual that was recently arrested could try to use the same arguement.

I'm not aware of any case law on the subject. A lawyer would have to be asked if the arguement holds any weight.