Strange Random Logon Attempts

[jbl4me]

In my logs for the past week or so...Ive been seeing things like what ive pasted below...I don't have any clue what they could be, each one has a different domain / username, and to me they are totally random.

Reason: Unknown user name or bad password
User Name: GWMARPOL$
Domain: MARPOL
Logon Type: 3
Logon Process: NtLmSsp
Authentication Package: NTLM
Workstation Name: GWMARPOL
Caller User Name: -
Caller Domain: -
Caller Logon ID: -
Caller Process ID: -
Transited Services: -
Source Network Address: -
Source Port: -

Yesterday I had:

Logon Failure:
Reason: Unknown user name or bad password
User Name: 2KSERVER$
Domain: ZIMPORTS
Logon Type: 3
Logon Process: NtLmSsp
Authentication Package: NTLM
Workstation Name: 2KSERVER
Caller User Name: -
Caller Domain: -
Caller Logon ID: -
Caller Process ID: -
Transited Services: -
Source Network Address: -
Source Port: -