Windows 8.1 Update has been available for a little while now, and today -- June 10 -- is the deadline for upgrading. From this point forward, Windows 8 and Windows 8.1 users will no longer receive any more Windows Updates until they upgrade to Windows 8.1 Update.
Today's deadline comes one month after the original cut-off date of May 13, although business users have the option of holding out until August 12.
If you have Automatic Update enabled you should find that Update is already installed. But if you are taking care of your updates manually, you will need to upgrade to the very latest version of Windows if you want to continue to receive security updates and other patches.
So you want to reap the benefits of the next Patch Tuesday, make sure you have your system fully up to date.