Microsoft offered super cheap Windows 8 Pro upgrade keys and users have been asking whether they can perform a clean installation and activate Windows 8 using the upgrade product key, and the answer is "No" and "Yes" !!

Confused!, well Microsoft will detect whether you upgraded or clean installed and block users from activating using the upgrade product key showing the error as below. But, users can still get the product key working by doing a little registry hack which will enable them to activate - this is not fair (or legal I guess).