If you insert a hyperlink with a custom protocol or even, say, the file:
protocol, Excel will generate a warning message:
"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?"
If you say you do want to continue, things proceed as expected.

I've got a program that inserts hyperlinks using a custom URL protocol into
cells. In 97-XP, users can click on the hyperlink, and my custom URL
protocol handler will get called and do what I like. Now users have to go
through an extra step of clicking through this warning. Although I
understand MS's concerns here, does anyone know how a user can elect to
trust my protocol handler and avoid this message?

Thanks,
Mark