Corruption or disclosure of sensitive user documents can be among the most lasting and costly effects of malicious software attacks. Many malicious programs specifically target files that are likely to contain important user data. Researchers have approached this problem by developing techniques for restricting access to resources on an application-by-application basis. These so-called "sandbox environments," though effective, are cumbersome and difficult to use. In this paper, we present a prototype Windows NT/2000 tool that addresses malicious software threats to user data by extending the existing set of file-access permissions. Management and configuration options make the tool unobtrusive and easy to use. We have conducted preliminary experiments to assess the usability of the tool and to evaluate the effects of improvements we have made. Our work has produced an intuitive data-centric method of protecting valuable documents that provides an additional layer of defense beyond existing antivirus solutions.