UPDATE: Steam has fixed the error and the beta can no longer be downloaded.
A beta version of Sonic the Hedgehog 4: Episode 2 has been released on sale just a couple of hours ago this afternoon on PC digital download service Steam. Various Steam users on our SSMB forum have been able to purchase and download the beta and then play through it. At the time of this article we’ve just heard that SEGA has now become aware of the leak and has erased discussion of it over on their official forums. We expect SEGA will plug the leak on Steam pretty soon.
Thanks to the Steam users at the SSMB for the heads up and to Nemain for the image!