Seems like we've come across a number of non-genuine versions of Microsoft XP in the last couple of weeks. What all of the PCs had in common is that they went into small repair shops for repair with Windows XP Home Edition on them and came out with XP Professional installed. Most of the customers didn't notice the difference between the two while one customer who did, was told by the repair shop that they "upgraded" Windows while it was in for repair.
The reason that most non-genuine versions of XP encountered are the Professional version is because of the existence of Volume License versions of XP Pro for use by businesses. A Volume License is a special version of a Windows OS, most commonly XP Pro, that is sold to big businesses, governments and educational bodies for installation on hundreds or thousands of PCs. Because it is not practical for such large numbers of PCs to go through the Windows activation procedure post-installation for each PC, a Volume License installation does not require activation. All Windows XP installations do require a product key, the 25-digit alpha-numeric code that must be entered from the certificate of authenticity during the installation process. However, if a product key corresponding to a volume license (a so-called Volume License Key or VLK) is entered then the installation does not require product activation.
What has happened in the past, and no doubt continues to happen, is that Volume License Keys are passed on from IT staff to individuals and they get into general circulation for use by less than scrupulous individuals. When Microsoft becomes aware of these they are blocked and marked as non-genuine in their database. Beginning April 25, 2007, Microsoft began distributing Windows Genuine Advantage Notifications as "critical update" KB905474 to Windows users. If you downloaded this update and have a blocked VLK installed on your PC you will get the nag screen that you have a non-genuine copy of Windows installed ever more. We expect to see more of these in the weeks to come.