.exe, .msi, .app, .bat, .cmd, .vbs, .js, and .ps1 extensions are examples of what kind of files?

Believe it or not but some people are actually creating and sending messages with attachments that will do your computer no good. Yes, you are correct; VIRUSES! There are a lot of file types in which a virus can reside. The most known are executables (programs) and scripts (automated processes).

A filename consists out of 2 parts; a name and an extension. The extension is the part of the filename after the dot. For instance the filename document.docx. Document is the name part and docx is the extension part. The last part decides how the file opens. In our example a docx file will open with Microsoft Word.

At the moment there is a limited (but not a definite) list of file extensions that are known to be potential viruses. Outlook takes no chances and blocks these files whether or not it contains a virus because Outlook is not a virus scanner and therefore cannot determine whether the file is safe or not. This is actually a good thing; even unknown viruses will be blocked this way! The downside of this is that occasionally you could receive a file that you know is clean but still can’t access. For instance; you receive a certificate, script or other program by e-mail.

Outlook informs you about any blocked attachments in the message header

Unblocking procedure

Before I tell you how you can still access those attachments, you must realize that you are creating a security risk on your computer this way. A good practice is to send these files in a compressed format (for instance zip or rar). This enables you to scan the file before unpacking and it will also take less inbox space and upload/download time! Another way to go would be to upload it to a cloud storage service like OneDrive or Dropbox and share it from there.

To unblock attachments involves changing the Registry. I strongly recommend to only edit the Registry when you actually receive a blocked attachment and when there is no other way to obtain that file again in a safer way (in a compressed format or via cloud storage) and you know for sure that the file is clean. Also, change back the Registry directly after you’ve saved the attachment. It probably sounds paranoid but you’ll be hitting yourself if you get infected because you “opened the door and invited the virus” yourself.

Alright, here goes;

1. Make sure Outlook is closed.
2. Open the Registry Editor;
   • Start-> type; regedit
3. Locate the following key
   • Outlook 2007
     [HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\Security]
   • Outlook 2010
     [HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook\Security]
   • Outlook 2013
     [HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Outlook\Security]
   • Outlook 2016, Outlook 2019 and Microsoft 365
     [HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Security]
4. Go to Edit-> New-> String Value and name the value Level1Remove (case sensitive!)
5. Double-click on the newly created value and enter the extension including the “dot” that you want to open in Outlook. For instance .exe
   If you need to enter more than one extension you’ll have to type separate them by a semicolon like this; .exe;.bat;.url
6. Press OK on the input box and close the registry editor
7. When you open now Outlook, the attachments which hold those extensions aren’t blocked by Outlook anymore.

To let Outlook block those extensions again, follow the instructions again but instead of creating the Level1Remove value delete it.

If you are not comfortable with manually editing the registry or prefer easier access to block/unblock attachments you can also use OutlookTools (free).

Easily unblock (and then block again) attachments with OutlookTools.

Important!
Change back the Registry settings directly after you’ve saved the attachment or you’ll leave a door open for infecting your computer with a virus!

List of blocked attachments

This is the list of file types that are blocked by Outlook (click here for the latest list published by Microsoft).

Extension	File type description
.ade	Access Project Extension (Microsoft)
.adp	Access Project (Microsoft)
.app	Executable Application
.asp	Active Server Page
.aspx	Active Server Page Extended
.asx	ASF Redirector file
.bas	BASIC Source Code
.bat	Batch Processing
.cer	Internet Security Certificate File
.chm	Compiled HTML Help
.cmd	DOS CP/M Command File, Command File for Windows NT
.cnt	Help file index
.com	Command
.cpl	Windows Control Panel Extension (Microsoft)
.crt	Certificate File
.csh	csh Script
.der	DER Encoded X509 Certificate File
.diagcab	Microsoft Support diagnostic tools
.exe	Executable File
.fxp	FoxPro Compiled Source (Microsoft)
.gadget	Windows Vista gadget
.grp	Windows program group file
.hlp	Windows Help File
.hpj	Project file used to create Windows Help File
.hta	Hypertext Application
.htc	HTML component file
.inf	Information or Setup File
.ins	IIS Internet Communications Settings (Microsoft)
.isp	IIS Internet Service Provider Settings (Microsoft)
.its	Internet Document Set, Internet Translation
.jar	JAVA archive file
.jnlp	Java Network Launching Protocol
.js	JavaScript Source Code
.jse	JScript Encoded Script File
.ksh	UNIX Shell Script
.lnk	Windows Shortcut File
.mad	Access Module Shortcut (Microsoft)
.maf	Access (Microsoft)
.mag	Access Diagram Shortcut (Microsoft)
.mam	Access Macro Shortcut (Microsoft)
.maq	Access Query Shortcut (Microsoft)
.mar	Access Report Shortcut (Microsoft)
.mas	Access Stored Procedures (Microsoft)
.mat	Access Table Shortcut (Microsoft)
.mau	Media Attachment Unit
.mav	Access View Shortcut (Microsoft)
.maw	Access Data Access Page (Microsoft)
.mcf	Manifest configuration file
.mda	Access Add-in (Microsoft), MDA Access 2 Workgroup (Microsoft)
.mdb	Access Application (Microsoft), MDB Access Database (Microsoft)
.mde	Access MDE Database File (Microsoft)
.mdt	Access Add-in Data (Microsoft)
.mdw	Access Workgroup Information (Microsoft)
.mdz	Access Wizard Template (Microsoft)
.msc	Microsoft Management Console Snap-in Control File (Microsoft)
.msh	Microsoft Shell
.msh2	Microsoft Shell
.msh2	Microsoft Shell
.mshxml	Microsoft Shell
.msh2xml	Microsoft Shell
.msh2xml	Microsoft Shell
.msi	Windows Installer File (Microsoft)
.msp	Windows Installer Update
.mst	Windows SDK Setup Transform Script
.msu	Windows Update file
.ops	Office Profile Settings File
.osd	Application virtualized with Microsoft SoftGrid Sequencer
.pcd	Visual Test (Microsoft)
.pif	Windows Program Information File (Microsoft)
.pl	Perl script file
.plg	Developer Studio Build Log
.prf	Windows System File
.prg	Program File
.printerexport	Printer backup file
.ps1	Windows PowerShell
.ps1xml	Windows PowerShell
.ps2	Windows PowerShell
.ps2xml	Windows PowerShell
.psc1	Windows PowerShell
.psc2	Windows PowerShell
.psd1	Windows PowerShell
.psdm1	Windows PowerShell
.pst	MS Exchange Address Book File, Outlook Personal Folder File (Microsoft)
.py	Python script
.pyc	Python script
.pyo	Python script
.pyw	Python script
.pyz	Python script
.pyzw	Python script
.reg	Registration Information/Key for W95/98, Registry Data File
.scf	Windows Explorer Command
.scr	Windows Screen Saver
.sct	Windows Script Component, Foxpro Screen (Microsoft)
.shb	Windows Shortcut into a Document
.shs	Shell Scrap Object File
.theme	Desktop theme file settings
.tmp	Temporary File/Folder
.url	Internet Location
.vb	VBScript File or Any VisualBasic Source
.vbe	VBScript Encoded Script File
.vbp	Visual Basic project file
.vbs	VBScript Script File, Visual Basic for Applications Script
.vhd	Virtual Hard Disk
.vhdx	Virtual Hard Disk Extended
.vsmacros	Visual Studio .NET Binary-based Macro Project (Microsoft)
.vsw	Visio Workspace File (Microsoft)
.webpnp	Internet printing file
.website	Pinned site shortcut from Internet Explorer
.ws	Windows Script File
.wsc	Windows Script Component
.wsf	Windows Script File
.wsh	Windows Script Host Settings File
.xbap	XAML browser application
.xll	Excel add-in
.xnk	Exchange Public Folder Shortcut

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Which file types have .exe as their extensions?

Which is an example of file format extensions?

What are the five examples of file extensions?