By using the ClickOnce implementation in Visual Studio Tools for Office, administrators can configure the trust prompt level to allow prompting, disable prompting, or require a trusted certificate. This configuration is done by using a registry key that controls access to the inclusion list.
If prompting is disabled, only solutions that have a trusted and known certificate can be installed. If the prompting level is set to Authenticode required, the solution must be signed with a certificate from a known authority, but it does not require a certificate that chains to a trusted root authority (a trusted certificate). If prompting is allowed, the solution could be signed with a certificate with an unknown identity. In this scenario, the trust decision is deferred to the end user, and a temporary certificate would be sufficient to install a solution.
For more information, see How to: Configure Inclusion List Security (2007 System) and Table 2, titled Prompting Level Registry Key Value Launch Effects, in Configuring ClickOnce Trusted Publishers.