Attachments -- Blocking, Reassociating and Stomping

By Drew Nicholson, dnicholson@OutlookExchange.com

Attachments are the bane of the E-mail administrator. Most viruses are propogated through attachements -- Melissa, Ha-ha, etc. Here's what happens -- when the attachment is emailed to a user, they open it, either because they think it's from someone they know, or because they're simply ornery -- and the virus is loaded.

There are several remedies for this. Both Trend and Sybari make products that will block known viruses. You can keep your local desktop av software up to date as well. But many administrators have taken to blocking whole sets of extensions. Here is a long, but not necessarily comprehensive list:

ADE, ADP, ASF, ASX, AUD, AVI, BAS, BAT, BIN, CHM, CMD, COM, CPL, CRT, CSS, DLL, EXE, HIV, HLP, HTA, INF, INF, INS, ISP, JS, JSE, JTD, LNK, MDE, MIDI, MOV, MP3, MPA, MPE, MPEG, MPG, MSC, MSI, MSP, MST, OCX, OFT, OVL, PCD, PIF, PL, PLX, REG, RS, SCR,SCT, SH, SHB, SHS, SYS, VB, VBE, VBS, VCF, VST, VXD, WAV, WSC, WSF, WSH,

Obviously, you may or may not need to allow some of these kinds of files to be downloaded. Each administrator needs to decide what's best for them.

In addition, there is a command you can run from a command prompt to "reassociate" an extension, so when a file of that extension is double-clicked, it opens in EDIT format, rather than running. From a command prompt, type:

C:\>assoc .ext=txtfile

where .ext is whatever extension you wish to "reassociate" and you'll get

.ext=txtfile


in response. Then, when you double click on any file of that extension, it'll open in whatever your default editor is (usually notepad)! This command works in WinNT and Win2k. If anyone knows how to get it to work in Win9x, let me know...

Below is a list of files blocked by default in the "security aware" Outlook XP. Unless configured differently using the ORK or implementing several reg hacks, MS-Outlook XP will disallow access to these attachments by default. Note that this does NOT keep the extensions from being emailed, simply that XP won't allow you access to the attachments. This is, therefore, a CLIENT SIDE and NOT a Server Side solution.

File extension File type

---------------------------------------------------

.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 Registration 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

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