"system administrator" in this context means any user who is a member of the
administrators group.

There is an account called "administrator" which is  built into all versions
of XP.  If someone
has gained access to your computer via this account, they could easily do
damage such as this
or worse.  Whether this happened or not is hard for me to say.

While you cannot delete the built in account, you can disable it (set it
such that it cannot be used), and you should
rename it to some less obvious name than Administrator.  Before you disable
this account, make certain
that you have an account of your own making which is a member of the
administrators group.

Jim