In addition to the above, you can remove their ability to access your computer across the network by removing their user right. You should also not share folders, run a Web server on your computer, run remote administration programs (see your domain admins), run antiviral software to prevent Trojans and apply file and folder access permissions. Nothing can stop a determined attacker forever, but you can certainly build in layers of security that will defend your data files from your fellow workers.
You should also seek help from your information security staff. If you are having a problem with fellow workers destroying data files or abusing system privilges, security should be made aware.
This was first published in August 2002