This is a very nice breakdown:

http://www.cyberciti.biz/faq/understanding-bash-fork-bomb/

Be careful running commands that you don't understand! I've been bitten by that before...

I don't know about linux (and I really should in this case as it's my 'field'), but at least on mac, you can restrict the number of child processes a process can spawn with `ulimit -u`:

    zooey:~ duane$ ulimit -u
    709