ShopTo. According to Eurogamer, the original listing promised an HD collection of the original Mortal Kombat, Mortal Kombat 2 and Ultimate Mortal Kombat (an updated version of Mortal Kombat 3). The original listing included a November 12th release date.
The listing raises some questions. For example, considering the franchise's history, shouldn't this be called the Mortal Kombat ... Kompilation? Additionally, the product was listed only for PS3 -- could it be exclusive to that platform? (Considering the perpetual success of Mortal Kombat on PlayStation Network, that would be somewhat unsurprising.)
A WB representative decided not to confirm nor deny the validity of the leak, simply stating "there has been nothing officially announced at this point." However, the rep did note that she will let us (and you!) know "if and when there is anything to announce."