Custom User Agent String Unavailable with Proxy Auto Configuration Script (182859)


The information in this article applies to:

  • Microsoft Internet Explorer version 6 for Windows XP
  • Microsoft Internet Explorer version 6 for Windows 2000
  • Microsoft Internet Explorer version 6 for Windows NT 4.0
  • Microsoft Internet Explorer version 6 for Windows Millennium Edition
  • Microsoft Internet Explorer version 6 for Windows 98 Second Edition
  • Microsoft Internet Explorer version 6 for Windows 98
  • Microsoft Internet Explorer 5.5 for Windows 2000
  • Microsoft Internet Explorer 5.01 for Windows 2000
  • Microsoft Internet Explorer 5.5 for Windows NT 4.0
  • Microsoft Internet Explorer 5.01 for Windows NT 4.0
  • Microsoft Internet Explorer 5.0 for Windows NT 4.0
  • Microsoft Internet Explorer 5.5 for Windows Millennium Edition
  • Microsoft Internet Explorer 5.5 for Windows 98 Second Edition
  • Microsoft Internet Explorer 5.01 for Windows 98 Second Edition
  • Microsoft Internet Explorer 5.0 for Windows 98 Second Edition
  • Microsoft Internet Explorer 5.5 for Windows 98
  • Microsoft Internet Explorer 5.01 for Windows 98
  • Microsoft Internet Explorer 5.0 for Windows 98
  • Microsoft Internet Explorer 5.5 for Windows 95
  • Microsoft Internet Explorer 5.01 for Windows 95
  • Microsoft Internet Explorer 5.0 for Windows 95
This article was previously published under Q182859
IMPORTANT: This article contains information about modifying the registry. Before you modify the registry, make sure to back it up and make sure that you understand how to restore the registry if a problem occurs. For information about how to back up, restore, and edit the registry, click the following article number to view the article in the Microsoft Knowledge Base:

256986 Description of the Microsoft Windows Registry

SYMPTOMS

Your custom User Agent string may not be available to an automatic proxy configuration script.

CAUSE

Internet Explorer always fetches an automatic proxy configuration script by using a standard User Agent string of "Mozilla/4.0 (compatible; MSIE x4. y;platform)."

RESOLUTION

WARNING: If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk. To resolve this issue, add a DWORD value named AutoConfigCustomUA to the following registry key and set its value data to 1:

HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings

Note: Versions of Internet Explorer that are earlier than version 5.0 do not support this registry value. If you experience this problem with a version of Internet Explorer prior to 5.0, obtain the latest version of Internet Explorer, and then set this registry value. This problem was first addressed with an Internet Explorer 4.01 hotfix that caused Wininet.dll to query the registry key described earlier to determine whether it should use the standard User Agent string or the custom User Agent string that it uses for other requests (such as the GET request for a Web page) when responding to an automatic proxy configuration script.

For Windows NT Workstation or Server 4.0:

Wininet.dll dated 3-4-98, size 369,424 bytes, version 4.72.3104.0 or later

For Windows 95:

Wininet.dll dated 3-4-98, size 370,448 bytes, version 4.72.3104.0 or later

The original Internet Explorer 4.01 hotfix is no longer available since Internet Explorer 4.x is unsupported, but this update to Wininet.dll is included with Internet Explorer 5.0 and later.

MORE INFORMATION

Internet Explorer uses a standard User Agent string of "Mozilla/4.0 (compatible; MSIE x.y; platform)." For example, the standard User Agent string for Internet Explorer 6 on Windows XP is Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1). Administrators can modify this standard string by using the Internet Explorer Administration Kit (IEAK) or by manually modifying the User AgentString value under the following registry key:

HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings

After you modify this User Agent String value, Internet Explorer appends the new string to the end of the standard User Agent string when responding to HTTP servers. However, Internet Explorer only presents the standard User Agent string to proxy servers during automatic configuration unless you set the registry value in the Resolution section of this article.
Modification Type:MajorLast Reviewed:9/18/2003
Keywords:kbprb KB182859
©2003 Microsoft Corporation. All rights reserved.