What happened there is no different than what happens when someone posts a spreadsheet with useful stuff here. Within minutes it will get destroyed or defaced.
The 'griefers' have definitely discovered HN. I suspect that some of them are people that took rejection by YC a bit harder than they should have, and that some others are simply here because they can't see a good thing without being tempted to try to destroy it.
Anything - and I really mean anything - that you put out there on the internet needs to be designed with abuse in mind, because no matter how small it is the abusers will seek it out and will try to destroy it.
That's something that you need to be aware of as much as you need to be a coder or a designer when you plan on making a living online.
Better get used to it.