Could something like this (http://www.cyberciti.biz/tips/linux-limiting-user-process.ht...) be quickly implemented on the server?

I think people must be brute-forcing level03 instead of figuring out how to calculate the index they need?! That could work but you won't know how address math/pointer math actually works. This isn't really fair to yourself, you'll be skipping out on understanding what a word size is.

But, for those uninterested in the minutiae of how it actually works if you are going to brute force this please compile this application on your OWN 64-bit system (gcc -g -o level03 level03.c) and run your nasty for() loop there so you aren't hosing the processes on this system!

Sociopaths...