It's a sitewide competition that the owner has done before with various vendors (most recently Innoken). There should be an X in the upper right hand side that you can click to make it go away.
Due to the site's "high disgust level" (to put it mildly) with floating pop ups that need to be x'd out all the time, it will probably only appear a couple times as you X it out, so if you want to participate in the givaway, open it and it will give you instructions on how to proceed, otherwise just X it out the first few times you see it, and it should stop stalking you, asking you about your
mods, telling you look fat in those pants, and etc.
Good luck!
Anna