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Viewing CHM Files Across Networks

Viewing CHM Files Across Networks

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Viewing CHM Files Across Networks

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Microsoft released a security patch that makes it impossible to view CHM files that are stored on a network drive (as opposed to CHM files stored on your own computer). The help file will appear, but instead of the topic text you will see an error message "this page cannot be displayed".


The security patch and its effects are fully described on Microsoft's web site at


If you trust all the computers on your LAN or intranet (and the people using them), you can lower the restrictions on the Local Intranet zone to allow CHM files to be displayed with the following steps:


1. Click Start, click Run, type regedit, and then click OK.

2. Locate and then click the following subkey:


If this registry subkey does not exist, create it.

3. Right-click the ItssRestrictions subkey, point to New, and then click DWORD Value.

4. Type MaxAllowedZone, and then press Enter.

5. Right-click the MaxAllowedZone value, and then click Modify.

6. In the Value data box, type 1, and then click OK.

7. Quit Registry Editor.


If this solution does not work for you, please see for alternatives.


The security update may also prevent you from opening CHM files that you downloaded from the Internet. To resolve this problem, click to clear the Always ask before opening this file check box in the Open File-Security Warning dialog box, and then click Open. Alternatively, right-click the file that you want to open, click Properties, and then click Unblock. See for more information.


If your customers are having problems accessing your CHM files, you have the following options:

1. Make them aware of the issues involving the security update

2. Make sure your software's installer installs CHM files locally rather than on the network. Then they will always work.

3. Use the WinHelp format instead of HTML Help (CHM). WinHelp HLP files are not affected by this security issue.




HHReg v1.2 - HTML Help Registration Utility


HHReg is a utility to register HTML Help (.chm) files on an individual Windows computer to make them available for viewing. Registration for HTML Help files is required since Microsoft issued a security patch for Microsoft Internet Explorer, disabling in general all HTML Help files that are viewed from a network drive.


HHReg removes this limitation by explicitly registering HTML Help CHM files in the Windows registry, making them available for viewing even when opened on network drives.




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