someone brute force attacking my computer or what? windows xp evt loaded with hundreds of error 680

Event Type:Failure Audit
Event Source:Security
Event Category:Account Logon 
Event ID:680
Date:8/13/2013
Time:5:40:53 PM
User:NT AUTHORITY\SYSTEM
Computer:Digningrmcmp
Description:
Logon attempt by: MICROSOFT_AUTHENTICATION_PACKAGE_V1_0
 Logon account:  support
 Source Workstation: Digningrmcmp
 Error Code: 0xC0000064


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

Microsoft writes that this is not important. however I'm worried as the "logon account" keeps on changing as if someone is trying to fish a username. Is this what it seems to be? someone attempting to brute force my computer or what? I have hundreds of these logon attempts.

Below is just a small sample of "logon account" names.

John, administrator, Administrator, owner, a, sql, david, support_388945a0, backup, root,