Implications of Setup Programs and EFS

If your users use the Encrypting File System (EFS) it is possible they have encrypted their temporary files directory, as recommended by Microsoft. You may have a little problem if your component creates temporary files in common locations such as the temporary directory, %TEMP%, and then moves them to the final location. Because the files are encrypted using the EFS key of the user account that set up the application, other users might be unable to use your program as they cannot decrypt the files and are denied access by the operating system. Setup programs should perform one of the following actions to ensure their component setup is not broken when used on systems encrypted with EFS:

Create your own random temporary directory
Create the files with the system attribute set (dwFlagsAndAttributes of CreateFile has FILE_ATTRIBUTE_SYSTEM set)
Detect that the %TEMP% directory is encrypted (use GetFileAttributes) and remove the encrypted bit from your files