Product Activation and Verification

Windows Genuine Advantage

While product activation and licensing servers are common for business and industrial software (especially software sold on a per-user basis for large sums of money), Windows XP gave many casual computer users their first introduction to it, under the name "Windows Genuine Advantage" (WGA). The system was introduced by Microsoft to curb unauthorized distribution of Windows XP.Activation requires the computer or the user to activate with Microsoft within a certain amount of time in order to continue using the operating system. If the user's computer system ever changes — for example, if two or more relevant components of the computer itself are upgraded — Windows may refuse to run until the user reactivates with Microsoft.
WGA comprises two parts, an activation/verification system based in part upon the computer's hardware, and a user notification system. WGA for Windows was followed by verification systems for Internet Explorer 7, Windows Media Player 11, and Microsoft Office 2007.
If the license key is judged not genuine, it displays a nag screen at regular intervals asking the user to buy a license from Microsoft. In addition, the user's access to Microsoft Update is restricted to critical security updates, and as such, new versions of enhancements and other Microsoft products will no longer be able to be downloaded or installed.
Common criticisms of WGA have included its description as a "Critical Security Update", causing Automatic Updates to download it without user intervention, its behavior compared to spyware of "phoning home" to Microsoft every time the computer is connected to the Internet, the failure to inform end users what exactly WGA would do once installed (rectified by a 2006 update), the failure to provide a proper uninstallation method during beta testing (users were given manual removal instructions that did not work with the final build), and its sensitivity to hardware changes which cause repeated need for reactivation in the hands of some developers.
Strictly speaking, neither the download nor the install of the Notifications is mandatory; the user can change their Automatic Update settings to allow them to choose what updates may be downloaded for installation. If the update is already downloaded, the user can choose not to accept the supplemental EULA provided for the Notifications. In both cases, the user can also request that the update is not presented again, but in any case, all newer Critical Security Updates will not install either. However this setting will only have effect on the existing version of Notifications, so it can appear again as a new version.