About once a month I go to Microsoft’s Windows Update website to manually check for security fixes. Last week the site prompted me to download new Update software in order to check for fixes. After I did that I now get prompted with a Continue button and the message:
To get updates, you must first validate your Windows software. Validation assures that you are using an authentic and fully licensed copy of Windows.
To disable their attempt at proving you’re a pirate:
Before pressing ‘Custom’ or ‘Express’ buttons paste this text to the address bar and press enter:
It turns off the trigger for the key check.
Why do *I* post this? Uh, no reason.
Update: XP: Get Updates No Matter What or Change your Invalid Product Key goes into more detail about this.