Uhh...with the amount of spyware on XP, that wouldn't surprise me one bit. I don't see how it could have happened though - I clean this machine regularly, and it's not in control of the firewall (my router does that). And I've never used the code for any other computer or given it away.
There are plenty of keygens out there for WinXP. Probably, you are one of the unfortunate souls who has a code that is likely to be generated by one of the "randomized" key generators. (I put random in quotes, because the keygens are rarely very random at what they generate.) I'm going to guess you bought this copy of WinXP shortly after it came out?
I've had this happen on several games that I purchased shortly after they came out. Within a month or so, someone had a duplicate of my CD Key... Yet I never gave mine out. Thanks, software companies for punishing the people who BUY software. :pissed:
