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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.

Extension

Description

.ade

Microsoft Access project extension

.adp

Microsoft Access project

.bas

Microsoft Visual Basic class module

.bat

Batch file

.chm

Compiled HTML Help file

.cmd

Microsoft Windows NT Command script

.com

Microsoft MS-DOS program

.cpl

Control Panel extension

.crt

Security certificate

.exe

Program

.hlp

Help file

.hta

HTML program

.inf

Setup Information

.ins

Internet Naming Service

.isp

Internet Communication settings

.js

JScript file

.jse

Jscript Encoded Script file

.lnk

Shortcut

.mdb

Microsoft Access program

.mde

Microsoft Access MDE database

.msc

Microsoft Common Console document

.msi

Microsoft Windows Installer package

.msp

Microsoft Windows Installer patch

.mst

Microsoft Visual Test source files

.pcd

Photo CD image, Microsoft Visual compiled script

.pif

Shortcut to MS-DOS program

.reg

Windows Registry entries

.scr

Screen saver

.sct

Windows Script Component

.shb

Shell Scrap object

.shs

Shell Scrap object

.url

Internet shortcut

.vb

VBScript file

.vbe

VBScript Encoded script file

.vbs

VBScript file

.wsc

Windows Script Component

.wsf

Windows Script file

.wsh

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:

Extension

Description

.286

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

.386

A device driver written for Windows 3.x

.vxd

Virtual device Driver, a program that emulates hardware

.dll

A Dynamic Link Library, contains reusable small routines

.ocx

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

.vbx

An early, 16-bit predecessor of ActiveX controls

.drv

A Windows or DOS device driver

.ovl

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

.scf

Windows Explorer Command

.sys

An extension to DOS, loaded when the computer boots

.qtx

A program that adds features to Apple's QuickTime program

.fot

Older TrueType font files. These are actually programs

.rom

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

.class

Java Applet (small program written in Java programming language)

.job

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.

Extension

Description

.htm

Web page, which may contain scripts

.html

Same as .htm

.htt

HyperText Template, which can contain same information as .htm

.doc

Microsoft Word document

.wll

Microsoft Word add-in

.dot

Microsoft Word template

.wiz

Microsoft Word Wizard

.xls

Microsoft Excel spreadsheet or worksheet

.xla

Microsoft Excel add-in

.xll

Microsoft Excel add-in

.xlt

Microsoft Excel template

.mdt

Microsoft Access add-in

.mdz

Microsoft Access database template/wizard

.pot

Microsoft PowerPoint template

.ppa

Microsoft PowerPoint add-in

.wpt

WordPerfect template

.wpm

WordPerfect macro

.mht

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.