Depending on how your browser in configured, you may see the message above when you attempt to access a custom page in your CRM system. This is caused by a change in the security level of the pages in the system. If you are using HTTPS for your system and have (for example) an IFRAME that is using HTTP, you will see this message everytime you attempt to access the page.
We can simply click 'No' on this message to display the custom page, but having to click this button everytime a custom page opens grows tiresome very quickly. Luckily for us, there is a simple browser setting change that we can apply to prevent these messages from appearing.
Go to Tools –> Internet Options –> Security Tab. Here select the proper zone under which your custom pages or the "HTTP" pages came. In my case, this was the Internet zone. When you have the proper zone selected, click the 'Custom Level' button.
Now go to Miscellaneous –> Display Mixed Contect and select "Enable" option as shown in the below screen shot.
Viola! No more prompts for your custom pages!