The non-minified source is pretty self-explanatory. It modifies a lot of the standard javascript functions. My favorite is the document.write(element) is modified to surround the element with <marquee> and <blink> tags and then write that to the DOM.
I like
Math.pow = function() { return "pow pow pow!"; }
To an extent, yes. I already looked at the source. But it just says to include evil.js on my site. How is that protecting my site from bandwidth thieves? Won't it also screw up my own site's functions?