Notice: This website is an unofficial Microsoft Knowledge Base (hereinafter KB) archive and is intended to provide a reliable access to deleted content from Microsoft KB. All KB articles are owned by Microsoft Corporation. Read full disclaimer for more details.

An overview of unsafe file types in Microsoft products

View products that this article applies to.

Support for Windows Vista Service Pack 1 (SP1) ends on July 12, 2011. To continue receiving security updates for Windows, make sure you're running Windows Vista with Service Pack 2 (SP2). For more information, refer to this Microsoft web page: Support is ending for some versions of Windows.

↑ Back to the top


Many Microsoft products use the concept of "unsafe file types" to help protect users from potentially malicious code that can be embedded in these files. This article provides an overview of unsafe file types and of the safeguards that Microsoft has created to help protect customers from unsafe file types.

↑ Back to the top

More Information

Many types of files are designed to let automated actions run during ordinary use of the file. Obvious examples of this functionality include program files (*.exe), batch files (*.cmd and *.bat), and script files (*.vbs and *.js). These files are designed for the sole purpose of executing commands. Less obvious examples are file types that allow for embedded script operations, such as Microsoft Access files (*.mdb) or macros in Microsoft Word files (*.doc) or in Microsoft Excel files (*.xls).

The ability to perform script actions in applications can be a very powerful productivity tool that gives customers great flexibility in how they apply Microsoft products to solve real-world problems. However, these same technologies can be leveraged by a malicious attacker to damage a user's computer. A common scenario occurs when a malicious attacker sends an unsafe file attachment in an e-mail message. When the recipient opens the file attachment, the malicious payload is delivered. Microsoft has adopted many strategies to help protect customers from threats that could be delivered in these types of files without losing the benefits that these file types offer.

Microsoft customers should be aware that opening unsafe types of files could cause malicious damage to computer systems. These files could contain viruses or Trojan horse programs and could be used to alter or to delete information that is stored on the computer. These files could also be used to send information that is stored on a computer to other computers. We recommend that customers only open these types of files after customers verify that the sender is trustworthy and that the sender intentionally sent the file. (Customers must verify that a file was not sent by a virus that is running on the sender's computer.)

For more information about Microsoft products that include safeguards to help protect customers from unsafe file types, visit the following Microsoft Web site to obtain the Understanding Executable Content in Microsoft Products white paper:

For more information, click the following article numbers to view the article in the Microsoft Knowledge Base:
Article numberArticle title
883260 Description of how the Attachment Manager works in Windows XP Service Pack 2
291369 Information about the Unsafe File List in Internet Explorer 6, 7, or 8
927117 Information about the unsafe file list in Microsoft Internet Explorer 5.01 Service Pack 4
291387 Using virus protection features in Outlook Express 6
262631 OL2000: Information About the Outlook E-mail Security Update
829982 You may receive an "Outlook blocked access to the following potentially unsafe attachments" message in Outlook
In some cases, Microsoft provides functionality that lets customers modify the list of files that may be unsafe.

Important We strongly discourage customers from removing file types from the default lists.

Sometimes, Microsoft receives reports of purported security vulnerabilities because of the ability of unsafe file types to perform malicious actions. Microsoft evaluates these reports on a case-by-case basis. However, Microsoft does not categorize a specific file type as a vulnerability merely because someone used the file type for malicious purposes.

Microsoft provides the following additional guidance to help protect customers from damage that may be caused by unsafe files.

For home users, visit the following Protect Your PC Web site: For IT Professionals, visit the following TechNet Security Center Web site: For information about how to avoid computer viruses that spread by using e-mail messages, visit the following Microsoft Web site: Customers who believe that they may have been affected by viruses or by Trojan horse programs may contact Microsoft Product Support Services. You can contact Product Support Services in North America at no charge. To do this, use the PC Safety line (1-866-PC-SAFETY). International customers can contact Product Support Services by using the methods that are described on the following Microsoft Security Help and Support for Home Users Web site:

↑ Back to the top

Keywords: kb, kbmustloc, kbtshoot, kbinfo, kbexpertiseinter, kbexpertisebeginner, kbsecurity, kbpubtypekc

↑ Back to the top

Article Info
Article ID : 925330
Revision : 4
Created on : 4/17/2018
Published on : 4/17/2018
Exists online : False
Views : 447