Who is this ... account?

After a few days since Vista Installation an unknown user appeared in my
Videos, Music and Pics folders. I formatted the HD, scared of some
intruders, and again anbther user is around. I do not know if it is the same
one because the name is a long series of numbers:

S-1-5-21-132779530-93896968-1742627343-1000

The fact is i can not delete this account from the security list, and even
there is a red question mark on top of the user icon.

Also in explorer the folders display the following: SHARED WITH: Unknown
Contact, ...

Maybe this is some kind of bug in Vista.
Thanks

On some of my shared folders and files I have the same thing.

On some of my shared folders and files I have the same thing.
The said files and folders are shared with my laptop.
I think this is why there is (in my case anyway) a question mark.
I might be wrong, but it seems to be a logical reason (in my case).

NIK

Hello,This number represents an account being granted access to that folder.

Hello,

This number represents an account being granted access to that folder.

In Windows, your user account (such as "Smitty") is represented internally
as a long string of numbers (like the one you mentioned). Therefore, a user
named smitty on one installation of Windows will have a different number
than a user named smitty on a different installation of Windows, even if
these installations of Windows are on the same computer.

So, if you look at the security on a file that was created on another
computer, created from a different installation of Windows, or you have
given yourself access to the file from another installation of Windows, you
will see a number instead of an account name, since that number represents
an account on another installation of Windows and is only meaningful from
that other Windows installation.


--
- JB
Microsoft MVP - Windows Shell/User

Windows Vista Support Faq
http://www.jimmah.com/vista/