Possible Hacked Scripts?

Hi,

We’ve been using your plugin for months on a site. Over the weekend we had a very strange iframe embed added to the bottom of every page of our site. We deemed your plugin responsible as when we disable it the iframe goes away.

Here’s a screen capture of the hack: https://snag.gy/TCzSya.jpg

Have you seen this before or do you have any idea how this is possible through your plugin?

Thanks