Chat window popping up on site

[Vanillas]

I have been with this site a couple of months but don't recall seeing that pop-up for the first several weeks. I'm sure it is what a previous poster said it was, namely a way for this (otherwise free) site to make money. Granted, it is annoying, but not as much as those on Cam 4, another free site. In short, I don't see anything sinister or underhanded behind it.