In the interest of a good argument, I will assert that all that have replied to this post are not entirely correct.
The idea of "rigorous unbreakability" is correct. This is what gives a cryptographic algorithm strength (or reliability). No one should trust the security of a crypto algorithm without its creators first explaining the details of how it works. If it is truly a strong algorithm, then it won't matter that the masses understand the process in its entirety (AES, for instance).
Further, security through obscurity is nonsense, unless I'm an immature script kiddie that only looks for ports on which a known service is running (i.e. ssh=TCP22). For realistic security implementations, one should always assume protection against the most aggressive techniques of penetration. Hence, that is why obscuring ports is worthless.
Finally, the priorities of an attacker once they have gained access will more than likely not be data destruction. The point of the attack will likely be to remain undetected so they can gather as much information from a victim's infrastructure or data as possible. If I'm a bad guy, the last thing that I want you to know is that I've gained access to your system. Then you'll only patch the hole I used and make it more difficult for me to get back in.