Found this over at Neowin: Today is talk like a pirate day and the crazy folks at Microsoft UK have issued a light-hearted press release having a jab at those who use pirated Microsoft products. Although the press release is a joke, Microsoft recently started an optional Windows Validation process on their download servers. At recent conferences before the release of XPSP2 several Microsoft representatives have hinted at possible PID blocking on other Microsoft applications. In simple terms if you have a pirated version of Windows XP and you install an updated application like Windows Media Player, that application will detect your pirated install and will not install. There are also rumours that Microsoft are cracking down on the pirates themselves. Earlier this week the largest seizure of counterfeit Microsoft software and components took place, worth $80 million. For now the pirates are laughing but it looks like Microsoft are beginning to laugh and I'm sure they'll have the last laugh. Read the whole story at Neowin.
Check the validation process yourself: Windows Media Encoder 9 Series
Read more about the validation process at Microsoft