Basically, I believe there would be two types of approaches to this problem: 1. Hook the file system to send notifications when a file is accessed 2. Hook a system event to give you a notification each time a file is opened. 3. Use the standard file commands to prohibit access The first method is by far the most troublesome and difficult, but will provide the most accurate, functioning results. You would need a low level access to the NTFS file system and be able to enumerate through currently open files. If the desired file is found in this enumeration, it is closed. The second method relies on the Windows OS to give you a notification when a file system event occurs. The most effective way to accomplish this would be to use some IFS element. IFS (Installable File System) is part of the Windows DDK and allows you to build file system filter drivers, which can capture different events. FileMon is one example from this type of application. The final option is the most easiest: when your application is started, you open the file in a non-exclusive mode, which means that all other attempts to access this file while your application has it open will fail. However, this means that only your application can access the file in question, and this approach will cause a system crash if used on critical system files. But for protecting application-specific files, this is the most effective one. For an example, see this article[^] -Antti Keskinen ---------------------------------------------- The definition of impossible is strictly dependant on what we think is possible.