Windows Product Activation (WPA) is the mandatory product registration system included in Microsoft's Windows XP, Office XP, and recent Office products (such as Word 2002 or Excel 2002) as a means of enforcing compliance with the company's End User License Agreement (EULA). Essentially a copy protection system, product activation creates an association between each copy of a product and the computer it is installed on, so that the software cannot be copied to other, unauthorized machines.
A product with WPA works normally when it is installed. However, an internal mechanism monitors the number of times you launch the product and the amount of time that has elapsed since you installed it. If you don't contact Microsoft to get a 50-digit activation key before you reach one of those limits, the WPA system will deactivate your software. Depending on the product, WPA will either limit the software's functionality or disable it completely. Office XP users, for example, can still access their data and can work with it in programs other than Office XP: for example, if a user's copy of Word 2002 is deactivated, they will still be able to view their files in Word and modify them in WordPerfect.
In comparison, Windows XP users that exceed the WPA limit (either a month or 30 operating system launches) are locked out of the operating system entirely. Beyond the stipulated grace period, someone attempting to log in to Windows sees a message: "This copy of Windows must be activated with Microsoft before you can log on. Do you want to activate Windows now? (Yes/No)" If the user clicks "Yes," the system guides them through the activation process. To get there on your own, click "Start," point to "Programs," "Accessories," and "System Tools" and then click "Activate Windows."
Microsoft claims that WPA's sole purpose is to control software piracy, and in particular, the type of software piracy they refer to as "casual copying," in which a single user with a single license to the software installs a product on several different machines. However, because WPA collects information about the user's computer, many are concerned about possible threats to privacy. Others have expressed anger at learning about WPA only after purchasing a product using it. According to Bill Gates, 17 million copies of XP were shipped in the three months after the product launched in late October 2001.