HomeXP Security (Hacking?)

From: Stacey (postmaster_at_witchytree.com)
Date: 06/30/03 

Date: Sun, 29 Jun 2003 18:27:26 -0700

Hi.

I'm at my parents and I randomly decided to check out
their security event viewer and we have a tonne of
anonymous log ons and access denied ones, like this:

Event Type: Failure Audit
Event Source: Security
Event Category: Logon/Logoff
Event ID: 529
Date: 6/22/2003
Time: 11:00:32 PM
User: NT AUTHORITY\SYSTEM
Computer: LAVALLIECOMP
Description:
Logon Failure:
         Reason: Unknown user name or bad password
         User Name: Administrator
         Domain: TANYA
         Logon Type: 3
         Logon Process: NtLmSsp
         Authentication Package:
        MICROSOFT_AUTHENTICATION_PACKAGE_V1_0
         Workstation Name: TANYA

My parents are a stand-alone and not on a network. How
can I track these anony log ons & attempts, or prevent
them from happening? And how did they find this PC?

Any linkies would be helpful too.

Thank you.