It's a secret message inserted inside "the architecture" of a website.
What's the defacing of a website ?
Changing the visual appeance of a website. Whether a prank or an attack, it is considered totally illegal, like graffiti in the street. This reward, if you select it, gives you access to all the previous rewards and the status of kissbanker of the lulz level 42.
What is the number 42 all about ?
This is the answer brought by the super computer Deep Thought to the ultimate question of Life, the Universe, and Everythingin the book, The Hitchkiker's guide to the galaxy by Douglas Adams.