Make Risky File Extensions Obvious

Some readers were confused by my June Windows Tips column, which advised leaving file extensions hidden (for creating on-screen sticky notes), while the same month's Internet Tips column recommended making file extensions visible (to identify potentially dangerous files masquerading as harmless file types).

Both approaches have their merits: 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.

Fortunately, you can have it both ways. 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. First, back up your Registry in case something goes wrong. Head over to "Step-By-Step: Care and Feeding of the Windows Registry" for step-by-step instructions. Now choose Start, Run, type regedit, and press Enter. Double-click HKEY_CLASSES_ROOT to expand the list of folders (which are called keys in Registry lingo). Within the HKEY_CLASSES_ROOT key, scan the list for a key named exefile (not .exe). With exefile selected in the left (tree) pane, right-click in the right pane and choose New, String Value. Type AlwaysShowExt (all one word) and press Enter. The right pane should now have an icon named AlwaysShowExt. Exit the Registry Editor (see FIGURE 2).

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. If you change your mind, you can reverse the effect by deleting the AlwaysShowExt icon from the exefile key.

For maximum security, repeat the previous steps for the following Registry keys in HKEY_CLASSES_ROOT: cmdfile, comfile (in Windows 2000 and XP only), batfile, and scrfile. If you're concerned about people sending you harmful script files, add the AlwaysShowExt icon to the following Registry keys: JSFile, JSEFile, VBEFile, VBSFile, and WSFFile.

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