The details it sends are the same as when you first activated Windows XP. It checks 7 items of hardware on the computer to make sure that the computer your registered when you activated the Product ID Number is still that computer. You are permitted 2 hardware changes without having to phone Microsoft. Having said that, the details drop off the Microsoft register after 6 months. It is looking for a Windows PID on more than one computer during any 6 month period. Windows Genuine Advantage also checks your PID with a list of known 'compromised' PIDs. All of the pirated versions of XP that come from cheap software vendors are corporate copies with shady PIDs.
My view is that whatever you feel about using pirated software, the software that actually makes your computer run, ought to be paid for.
You need Windows Updates to fix security issues. If you have a genuine copy of Windows, you have nothing to fear.
http://www.microsoft.com/genuine/facts.aspx?displaylang=en
WGA and data collection
None of the information collected by WGA will be used by Microsoft to personally identify or contact you. To help you validate your software, the WGA tools must collect a certain amount of configuration information from your computer. The data collected includes:
Computer make and model.
Version information for the operating system and software using Genuine Advantage.
Region and language setting.
A unique number assigned to your computer by the tools (Globally Unique Identifier or GUID).
Product ID and product key.
BIOS name, revision number, and revision date.
Volume serial number.
Just details about your computer hardware and your copy of Windows. Also says
As standard procedure, your Internet Protocol (IP) address is temporarily logged when your computer connects to a WGA website or server. These logs are routinely deleted.
Once you have Validated, that's it. A small file is placed on the computer that tells the Windows Update Server you have passed and that's the end of it.
There used to be a trick that if you failed validation, the URL said 'passed=false' of similar? You just changed the URL to passed=true and pressed the enter key.
If you do fail Validation, all the get is a little message box near the clock offering you the chance to buy a new copy. If Validation fails and you do have a legitimate copy, there is a department to help you. I have a contact name if you need it.
