Surely, If you have a Micrsoft product, for which you do not have a legit key, then axiomatically, you must have obtained it, under most circumstances, from a non authorised source? If you had such a key, you would not have the need to play with the expiry date. The legal point of messing with the expiry date is immaterial. If you are referring only to builds, which "semantically" speaking, is not Windows 7, then, on the expiry date, it will be flagged as illegal by MS. It will become disfunctional, unless you apply a further hack - which is illegal.