A computer in a network has an operating system. The operating system is configured to prevent running of software not identified in a list of approved software referred to as a white list. Software absent from the list is prevented from running by the operating system. The network has a server which determines, for each item of software on the white list, the administration rights of the users of computers having that item of software. If a white listed software item is present on one or more computers used by users without admin rights, then the admin rights of any user of other computers having the same white listed software item are withdrawn by instructions sent by the server to the computer.
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