Having file extensions visible can make certain malicious programs in your e-mail in-box more obvious. For example, showing a file attachment such as picture.jpg.exe, which would otherwise have the harmless-looking name picture.jpg. On the other hand, displaying all file extensions all the time looks ugly, makes file names more difficult to read, and increases your likelihood of changing a file's extension accidentally when renaming it. With a little editing of the Windows Registry, you can make Windows display only the file extensions of executable files, which you're less likely to rename or interact with directly. Follow these steps:
1. Click on the Start button and select Run 2. Type in 'regedit' and press OK 3. Double-click on the 'HKEY_CLASSES_ROOT' key 4. Scroll down the list to the 'exefile' key 5. Right-click in the right pane and select 'New->String Value' 6. Type in 'AlwaysShowExt' and press OK
You may need to restart Windows to see the effect, but from now on, all application files will have their .exe extensions visible in folder windows and other programs that display file names, even when 'Hide extensions for known file types' is selected.