Repeative event 538, 540 ANONYMOUS LOGON

Hi,

I got a windows 2003 web edition running in a webhosting company, this
computer is stand alone, not member of any domain.
Lately im getting alot event 538 and some seconds after a 540 event in the
event viewer.
What concerns me is that this is under a Anonymous user, should i be scared
or is this a normal issue

--------------------------------------------------------------------------
User Logoff:
User Name: ANONYMOUS LOGON
Domain: NT AUTHORITY
Logon ID: (0x0,0x2D6BE6)
Logon Type: 3


For more information, see Help and Support Center at
http://go.microsoft.com/fwlink/events.asp.
--------------------------------------------------------------------
Successful Network Logon:
User Name:
Domain:
Logon ID: (0x0,0x2D6EF9)
Logon Type: 3
Logon Process: NtLmSsp
Authentication Package: NTLM
Workstation Name: HNPC4
Logon GUID: -
Caller User Name: -
Caller Domain: -
Caller Logon ID: -
Caller Process ID: -
Transited Services: -
Source Network Address: 81.173.236.114
Source Port: 0


For more information, see Help and Support Center at
http://go.microsoft.com/fwlink/events.asp.
--------------------------------------------------------------------

How can i prevent this?