Potentially "Unsafe" Filetypes

** Updated 6/26/2000

The following list contains the types of files that can contain programs, and which can, if opened or run, make changes to your disk drive's contents. Because of this ability, these files are potentially "unsafe", meaning they could do harm. Open these files with caution. Always know the source of the file, and its purpose.

For more information, read:

First, here's Microsoft's list of potentially "unsafe" files. These are the files that cannot be received as email attachments, after you install the "Security Update" for Outlook 2000 and Outlook 98. These types of files, and others we'll see in a moment, are highlighted by Karen's Directory Printer.

Updated 6/26/2000

This "classic" list is not a complete accounting of the modern filetypes that might feature unsafe automation.




Microsoft Access project extension


Microsoft Access project


Microsoft Visual Basic class module


Batch file


Compiled HTML Help file


Microsoft Windows NT Command script


Microsoft MS-DOS program


Control Panel extension


Security certificate




Help file


HTML program


Setup Information


Internet Naming Service


Internet Communication settings


JScript file


Jscript Encoded Script file




Microsoft Access program


Microsoft Access MDE database


Microsoft Common Console document


Microsoft Windows Installer package


Microsoft Windows Installer patch


Microsoft Visual Test source files


Photo CD image, Microsoft Visual compiled script


Shortcut to MS-DOS program


Windows Registry entries


Screen saver


Windows Script Component


Shell Scrap object


Shell Scrap object


Internet shortcut


VBScript file


VBScript Encoded script file


VBScript file


Windows Script Component


Windows Script file


Windows Script Host Settings file

Microsoft's latest list can be found on their web site at http://support.microsoft.com/support/kb/articles/Q262/6/31.html.

In addition, the newest Directory Printer highlights these additional types of executable files:




A device driver written for Windows 2.0 and 3.x real mode


A device driver written for Windows 3.x


Virtual device Driver, a program that emulates hardware


A Dynamic Link Library, contains reusable small routines


An ActiveX control, a small program used by other programs.


An early, 16-bit predecessor of ActiveX controls


A Windows or DOS device driver


A type of DOS program file, similar to Windows .DLL files


Windows Explorer Command


An extension to DOS, loaded when the computer boots


A program that adds features to Apple's QuickTime program


Older TrueType font files. These are actually programs


A copy of a program normally stored in ROM (Read-Only Memory)


Java Applet (small program written in Java programming language)


A list of programs to be run at a specific time

Directory Printer also highlights several types of files that can contain scripts or other types of small programs. Some scripts can do harm directly, while others can call DLLs and other types of executable files, to do damage.




Web page, which may contain scripts


Same as .htm


HyperText Template, which can contain same information as .htm


Microsoft Word document


Microsoft Word add-in


Microsoft Word template


Microsoft Word Wizard


Microsoft Excel spreadsheet or worksheet


Microsoft Excel add-in


Microsoft Excel add-in


Microsoft Excel template


Microsoft Access add-in


Microsoft Access database template/wizard


Microsoft PowerPoint template


Microsoft PowerPoint add-in


WordPerfect template


WordPerfect macro


Microsoft Internet Explorer single-file HTML archive

Change History

  • Thanks to reader Bob Dietz for the addition of the .wll and .xll file types.
  • Thanks to reader Tim McGowan for the addition of the .wpm and .wpt file types.
  • Thanks to reader Dan DeYoung for the addition of the .mht file type.
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