Outlook and Attachment Security

Although you can unblock any or all the file types, you should unblock only the file types that you really do need or use other methods to retrieve the attachments.. Many corporate firew

[ Team LiB ]

Outlook and Attachment Security

Some of most common attachments you receive, such as JPG and GIF images, are

entirely safe Others, such as Word or Excel documents, are usually safe but could carry macro viruses Other attachments, including those with exe, js, and pif extensions, might be safe, but they're just as often viruses Because it's impossible to know for sure, it's important that you not only install a virus scanner, but also use its autoprotect feature and keep the virus signatures current You should never open files you aren't expecting, even if your antivirus scanner gives them a clean bill of health—the virus might be too new to be in your virus definitions

Just in case you're lax when it comes to keeping your antivirus scanner up-to-date,

Outlook offers some built-in protection against email viruses, including blocking all file types that have the potential to carry viruses and are executable Although you can

unblock any or all the file types, you should unblock only the file types that you really do need or use other methods to retrieve the attachments

Many corporate firewalls block the same extensions that Outlook

blocks, and you might have to change the extension or zip the file

before sending attachments to some contacts If you'd like all of your

attachments zipped before sending, look for ZipOut, the WinZip

Outlook add-in or other utilities at http://www.slipstick.com

When you send blocked file types as attachments, you should get in the habit of changing file extensions to a safe, nonexecutable type or zipping the file Outlook 2003 won't warn you when you attach a blocked file type, but it will warn you before you send it, as shown

in Figure 6.5 Choose No, zip or add an underscore to the filename, and then reattach This ensures that the person you send it to can access it also

Figure 6.5 When you send attachments that could carry viruses, Outlook alerts you before sending If you edited your Registry to allow some file types, you won't see

the warning when you send these file types

Blocked Attachment File Types

When you receive a file with any of the extensions listed in Table 6.1, Outlook hides the attachment from you to prevent you from opening it and infecting your computer system

In reality, you can still retrieve the attachment in several ways, including editing the Registry to allow access to a specific file type, accessing your mailbox using a different mail program, or asking the person to zip the file and resend it

Table 6.1 File Attachment Types Blocked by Outlook 2003

.hta HTML program

.lnk Shortcut

.pcd Photo CD image or Visual Test compiled script

.prf Microsoft Outlook Profile Settings

.vb VBScript file

.wsh Windows script host settings file

.xsl XML file that can contain script

When you receive a message that contains a blocked attachment, Outlook places the text shown in Figure 6.6 in the message header The attachment icon is visible and all

messages with blocked attachments are included in the Large Messages Search Folder

Figure 6.6 Outlook's InfoBar alerts you to the fact that a blocked attachment is in

the message and includes the filename

Accessing Blocked Attachments

Many people find it easiest to edit the Registry and always allow some file types,

especially when they use the Attachment Options add-in from

http://www.slovaktech.com

Editing the Registry to allow all files isn't the brightest idea in the

world and could result in a virus infection For this reason, unblock

only the extensions for the attachment types you need to access

regularly, not all the file types If you don't normally get any blocked

attachment types, remove or rename the level1remove key when you

save the attachment you need

Outlook is programmed to block certain file types that Microsoft calls Level1

attachments These attachment types are considered dangerous Less dangerous

attachments are Level2 attachments and have to be saved to the hard drive before

opening You can move Level1 attachments to Level2 by editing the Registry You cannot remove attachment types from Level2

If you'd like to edit the Registry to add the Level1Remove key yourself:

1 Open the Registry Editor and navigate to

HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Outlook\Security

2 Right-click on the right pane and choose New, String Value

3 Enter Level1Remove for the name of the new value

4 Double-click on Level1Remove value name and enter the extension of the file types that you don't want blocked, in mdb format If you're unblocking multiple file types, separate the extensions with semicolons and don't use spaces, as in .pst;.prf

Exit the Registry Editor and restart Outlook You can now save the files you unblocked to your hard drive and open them (see Figure 6.7)

Figure 6.7 Add the Level1Remove key so that you can access blocked attachments.

If you want to force yourself always to save certain file types to the

hard drive before opening, add their extensions to the Level1Remove

value and force them to be considered Level2 attachments

You should encourage people to zip files before sending them Not only does this enable you to leave the extensions blocked, but it also reduces the size of the message

[ Team LiB ]