Filesystem permissions (well, restrictions, actually)
If the permissions on the removeable media use only
standard users or user groups (eg, Administrator,
Administrators, SYSTEM, Users, etc.) then you can access
the data on any NTFS system. If you use specific user IDs,
then the other systems will only see an unidentified GUID.
I should have been more clear.
So let's say Alice is a sysadmin on Artichoke, which is
running Windows Server 2003. Alice pops a large removable
disk of some kind into the drive on Artichoke, creates an
NTFS filesystem on it, and uses it to back up the contents
of "Documents and Settings", including permissions. Alice
then unmounts the disk, labels it with a date and "Documents
and Settings Backup", then she sticks it back in to check on
how the permissions work. She logs in as Xosha, which is a
limited user account, and tries to read some private files
that are owned by Administrator, but the system won't let
her. Alice now believes the backup is secure, so she logs
out, takes out the disk, and entrusts it to Bob, who is
supposed to store it offsite, in case there's ever some kind
of building-level disaster.
Bob, strapped for cash and disgruntled, clandestinely sells
the disk to George, who works for a rival company. George
takes the disk to *his* computer, where he *has*
administrative privileges, and proceeds to read all of the
unencrypted data on the disk. George may mount the disk
on a Windows system at his company, or he may mount it
on his FreeBSD laptop the minute he gets it from Bob, or
he might take it back to the office and use his Solaris
workstation to mount it. It doesn't matter; any way you
look at it, the security of the data is compromised.
Do not trust ownerships and privileges on removable media.
Ownerships and privileges on removable media are insecure.
If you need to prevent unauthorized people from reading
anything you put on removable media, encrypt it, or store
it in a secure location.