It has been known in the free versions that these hidden ads are there. They called it sponsors ads. As the other poster has stated, you have to find the hidden code in the files. But be aware that this might not be legal under any EULA that they include. I know these items are being released under GPL, but that does not mean that you can just rip the code out, if they made an issue on it.

I have done some mods that help to prevent these on our sites. Though I do provide a link back to here.