ACL Problem: "domain\administrator" permissions allows "computer\administrator" access

I don't know what is going on but I have shares that can be accessed by non-domain-joined computers via the local administrator account.

Removing domain\administrator removes the problem
Adding domain\domain admins creates the problem
adding domain\administrator creates the problem

From a random computer:
computername\administrator has access
computername\otheradministrator has no access

FYI the only other entry in the ACL is SYSTEM (full control)

Domain Functional level is Server 2003
Any clues would be appreciated.
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Radhakrishnan RSenior Technical LeadCommented:
Could you check whether the computer\administrators has allow access for this folder, if so, the local admin can able to access the shares.
Also, take the ownership of the shares and remove the permissions which is not required and see whether it's working.
subversivetechAuthor Commented:
No, only domain\groups are present in the ACL. Share permissions are set to "everyone" allow , but this is common practice and what I have always done. I rely on the ACL for security, not share permissions. Ownership is "domain admins"
Miguel Angel Perez MuñozCommented:
Domain Admins are the owner of folders and can access to them. Change owner or add a NTFS deny on ACL to prevent access.
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subversivetechAuthor Commented:
My issue is at the moment, anybody can walk into the office with a random computer (even the cleaner) and plug into the LAN. If they log in using "administrator" then bingo, they can access the shares. This is not as it should be "obviously". See screenshot of my ACL.
subversivetechAuthor Commented:
OK I started testing the administrative shares, eg, \\server\c$ and found they were accessible too. I changed the domain\administrator password and the problem went away.

Obviously if you use the same password for newcomputer\administrator as domain\administrator then the computer\administrator account seems to be able to impersonate the domain\administrator account, even if the computer is not joined to the domain! That is a surprise but not a real problem I guess.

All is well that ends well.

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subversivetechAuthor Commented:
Worked it out with some experimentation.
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Windows Server 2008

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