From what I understand (from here on Toms), kinguin is not legit. Windows may work for a while, but if Microsoft discovers the product key has been used before (for example when it does an update), it could de-activate Windows. Whether this will happen in one week, one month, or longer can't be determined. Maybe Microsoft isn't interested in de-activating products it no longer sells, like Windows 7, but there is always a risk. If you really need Windows 7, your best bet is to buy a boxed copy from a retailer, if they still have any in stock. (Best Buy, Fryes, MicroCenter, etc.)