In the old days, infected boot floppy disks were the most common way computer viruses were spread. Today, e-mail is by far the most common infection mechanism. Viruses range from mostly harmless (but irritating) to severe, sometimes causing irreparable damage to your system. Worms are a more recent variation, spreading across the Internet primarily through e-mail and by exploited operating system flaws. Worms can bog down a system by consuming the majority of the system’s resources, and they can cause the same types of damage as viruses.
Outlook 2007 provides protection against viruses and worms by letting you block certain types of attachments that are susceptible to infection. This prevents users from opening attached files that could infect their systems and execute malicious code on a user’s system to damage or steal data. Executable programs (.exe, .com, and .bat files) are also good examples of attachments that are primary delivery mechanisms for viruses. Many other document types are equally susceptible—HTML documents and scripts, for instance, have rapidly become favorite delivery tools for virus terrorists. Outlook 2007 provides two levels of protection for attachments, Level 1 and Level 2. The following sections explain these two levels, the file types assigned to each, and how to work with attachments.
Level 1 attachments are those that are common vectors for infection, such as executable (.exe) files. When you receive a message containing an attachment in the Level 1 group, Outlook 2007 displays the paper clip icon next to the message header, indicating that the message has an attachment, just as it does for other messages with attachments. When you click the message header, Outlook 2007 displays a message indicating that it has blocked the attachment.
You cannot open Level 1 attachments that are blocked by Outlook 2007. You can open and view the messages, but Outlook 2007 disables the interface elements that otherwise would allow you to open or save the attachments. Outlook 2007 displays a message in the InfoBar informing you that the attachment has been blocked and cannot be opened, as shown in Figure 34-1. If you forward a message with a blocked attachment, Outlook 2007 strips the attachment from the forwarded message.
Note
For details on how to open attachments that have been blocked by Outlook 2007, see "Opening Blocked Attachments" later in this chapter.
Table 34-1 lists the file name extensions for Level 1 attachments.
Table 34-1. Level 1 Attachments
File Name Extension | Description |
|---|---|
.ade | Access project extension |
.adp | Access project |
.app | Executable application |
.asp | Active Server Page |
.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® |
.com | Command |
.cpl | Windows® Control Panel extension |
.crt | Certificate file |
.csh | csh script |
.der | DER encoded X509 certificate file |
.exe | Executable file |
.fxp | FoxPro compiled source |
.hlp | Windows Help file |
.hta | Hypertext application |
.inf | Information or setup file |
.ins | Internet Information Services (IIS) Internet communications settings |
.isp | IIS Internet service provider (ISP) settings |
.its | Internet document set; Internet translation |
.js | JavaScript source code |
.jse | JScript® encoded script file |
.ksh | UNIX shell script |
.lnk | Windows shortcut file |
.mad | Microsoft Access module shortcut |
.maf | Microsoft Access file |
.mag | Microsoft Access diagram shortcut |
.mam | Microsoft Access macro shortcut |
.maq | Microsoft Access query shortcut |
.mar | Microsoft Access report shortcut |
.mas | Microsoft Access stored procedures |
.mat | Microsoft Access table shortcut |
.mau | Media attachment unit |
.mav | Microsoft Access view shortcut |
.maw | Microsoft Access data access page |
.mda | Microsoft Access add-in; Microsoft MDA Access 2 workgroup |
.mdb | Microsoft Access application; Microsoft MDB Access database |
.mde | Microsoft Access MDE database file |
.mdt | Microsoft Access add-in data |
.mdw | Microsoft Access workgroup information |
.mdz | Microsoft Access wizard template |
.msc | Microsoft Management Console snap-in control file |
.msh | Microsoft shell |
.msh1 | Microsoft shell |
.msh2 | Microsoft shell |
.mshxml | Microsoft shell |
.msh1xml | Microsoft shell |
.msh2xml | Microsoft shell |
.msi | Microsoft Windows Installer file |
.msp | Microsoft Windows Installer update |
.mst | Microsoft Windows SDK setup transform script |
.ops | Microsoft Office system profile settings file |
.pcd | Microsoft Visual Test |
.pif | Windows program information file |
.plg | Microsoft Developer Studio® build log |
.prf | Windows system file |
.prg | Program file |
.pst | Microsoft Exchange address book file; Outlook personal folder file |
.reg | Registration information/key for Windows 95/98; registry data file |
.scf | Windows Explorer command |
.scr | Windows screen saver |
.sct | Windows script component; FoxPro screen |
.shb | Windows shortcut into a document |
.shs | Shell scrap object file |
.ps1 | Windows PowerShell |
.ps1xml | Windows PowerShell |
.ps2 | Windows PowerShell |
.ps2xml | Windows PowerShell |
.psc1 | Windows PowerShell |
.psc2 | Windows PowerShell |
.tmp | Temporary file/folder |
.url | Internet location |
.vb | Visual Basic Scripting Edition (VBScript) file; any Visual Basic source |
.vbe | VBScript encoded script file |
VBScript script file; Visual Basic for Applications (VBA) script | |
.vsmacros | Microsoft Visual Studio® .NET binary-based macro project |
.vsw | Microsoft Visio® workspace file |
.ws | Windows script file |
.wsc | Windows script component |
.wsf | Windows script file |
.wsh | Windows script host settings file |
.xnk | Exchange public folder shortcut |
Outlook 2007 also supports a second level of attachment blocking. Level 2 attachments are defined by the administrator at the server level and therefore apply to Exchange Server accounts, not to Post Office Protocol 3 (POP3), Internet Messsage Access Protocol (IMAP), or Hypertext Transfer Protocol (HTTP)–based accounts. Because the Level 2 list is empty by default, no attachments are blocked as Level 2 attachments unless the Exchange Server administrator has modified the Level 2 list.
You can’t open Level 2 attachments directly in Outlook 2007, but Outlook 2007 does allow you to save them to disk, and you can open them from there.