What does it mean that I have an Account Known in the properties under security tab under title Group or User names for the shared folder? Does that mean some unknown person has permissions to my shared folder? Is this a security issue? Screen clipping taken: 2/6/2007, 7:48 AM

This normally happens when a SID cannot be mapped to an account name. It normally happens in one of the following two scenarios: 1.a useraccount was granted explicit rights to the resource then deleted and for some reason the rights didnt go with it 2. A user from a trusted Domain / Forest was granted priviledges to the resource and the trust has since been removed or broken in one way or another.

Thank you for the answer. I assume I don't have anything to worry about?

assumably you have nothing to worry about if one of the mentioned scenario's is true, and you can safely remove the user from the security properties.