Copies of Windows 8 Pro are freely available from Microsoft’s website for anyone who wants to try out the operating system. Normally, the software would expire after 180 days, a period that is meant to allow Volume Licensing customers to automate and manage the activation process. But a loophole in the company’s Key Management System allows anyone to legitimately activate their copy of Windows 8 permanently, for free.
The goof centers around the Windows Media Center upgrade that’s being for free offered by Microsoft themselves until January 31 next year. Specifically, when entering the add-on key, Microsoft’s Key Management System will let you fully activate your copy of Windows 8 without running a validity check for the product key of the underlying system the Media Center add-on is being installed on.
To get a free Media Center key all users need to do is request it from Microsoft’s website using any email address. Once the code is in your inbox, do a search for “Add features to Windows 8” under Settings, click on it and enter the product key. Media Center will download and install, and after your system comes back from a reboot, you’ll be able to use the same upgrade product key to activate Windows.
With this your copy of Windows 8 will become fully active and 'legitimate', which you can verify in the activation window where it should read “Windows is activated” instead of “Windows is activated until…”.
The method has been confirmed to work by several news outlets. I tried it as well but upon requesting a Media Center key the site responded it will be emailed to me “within 24 hours” -- I can’t tell if the wait period is standard or if Microsoft is moving to patch the flaw by implementing a check for the underlying system.