When you try to open a link that uses a custom protocol handler in a 2007 Microsoft Office system application, the following security prompt appears:
Microsoft Office has identified a potential security concern. This location may be unsafe. :// Hyperlinks can be harmful to your computer and data. To protect your computer, click only those hyperlinks from trusted sources. Do you want to continue?
Additionally, you have to click YES to continue. However, you cannot disable this notice.
This issue occurs because the 2007 Office system does not give the user a way to enable trust to customized protocol handlers.
To resolve this problem, apply the following hotfix package:
981041 Description of the 2007 Office system hotfix package (Mso-x-none.msp): April 27, 2010
Warning Serious problems might occur if you modify the registry incorrectly by using Registry Editor or by using another method. These problems might require that you reinstall the operating system. Microsoft cannot guarantee that these problems can be solved. Modify the registry at your own risk.
To activate this hotfix, create a registry sub key with the name custom_prot: at the following location:
HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\12.0\Common\Security\Trusted Protocols\All Applications\where custom_prot: is the actual protocol handler prefix.
For example, if you want to add an xyz: protocol handler, the subkey should appear as follows:
HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\12.0\Common\Security\Trusted Protocols\All Applications\xyz:Note: the colon (:) character should be included at the end of the protocol handler name. If any registry subkeys in the path shown above do not exist, you must manually create them.
Alternatively, you can also disable the security warning from being displayed for all hyperlink protocols. For more information, please see the following article in the Microsoft Knowledge Base:
925757 How to disable hyperlink warning messages in 2007 Office programs and in Office 2010 programs
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.