Indeed, hacking is pretty easy. There is a security leak in "4images 1.7.3" (the software used by localarcade). A hacker finds this info on a hacker list or something. Then you start google and you search for "Powered by 4images 1.7.3". Presto, a hack and a whole list of possible victims.
I usually try to make sure that from the website it's not obvious which software it uses. Obviously one should also make sure to apply all security patches as soon as possible, but when it's a hobby project people don't often have the time.