Most people don't realise that there pc isn't secured with XP, it's not tha your normal ADMIN has an pass that you're save.
You must put an password on your SYSTEMADMIN
Just follow the next steps:
Start = > Run => %SystemRoot%\system32\compmgmt.msc /s => ok
In the left side panel:
Local Users and groups = > users => right side you RIGHT-CLICK an ADMINISTRATOR => Set Password
Seems to be stupid, but it wil secure you to al amateur hackers.