MS stopped supporting my version of XP pro over a year ago when they started their authenticity certification checks.
Seems the version I bought (on e-bay) was either a copy or previously licensed. Now MS won't support it at all, no upgrades, no service packs, nothing. It still works just fine.
I un-installed the authenticity check but can't install any upgrades unless that authenticity check thing is installed and running.
They offered to sell me a new copy for some unreasonably high price, I said no thank you I already bought and paid for a copy.
Besides, all they were going to do was to sell me a license, not a copy.
Now if someone wanted to sell something that would bypass that authenticity check ....
j/k