Hi there. Yeah this is a pain.
Quote: "1. It appears that I downloaded and installed it through my browser. How do I check?"
Open your browser and open up Internet Options. Under IE, that is done by clicking on the cog and then on "Internet Options" from the menu. Go to the "Content" tab and click on the "Certificates" button under the certificates heading. Your code signing certificate (should be from Comodo if it's from AppUp) should be in the list.
Quote: "2. It says to download and backup. How do I do this?"
Continuing from the previous question.. Select the Comodo certificate and click "Export". Go through the wizard which will export and save your certificate as a pfx file. Now you have it as a file, you can back it up as normal (ie on a USB stick etc.).
Quote: "3. How do I use this? Do I use it when I compile my MSI, or do I somehow upload it into my AppUp Application?"
You use the certificate after you have created the MSI. You can do this at the command line but I prefer to make up a batch file - it will save you some typing if you have to redo it! So the code you want in your batch file is something like this:
cd "C:\Program Files (x86)\Microsoft SDKs\Windows\v7.0A\bin\"
signtool sign /v /f path\to\certificate\certificate.pfx /p password path\to\msi\msi.msi
pause
Obviously you'll need to adjust the addresses as appropriate for your machine. And then this to verify that it has been signed:
cd "C:\Program Files (x86)\Microsoft SDKs\Windows\v7.0A\bin\"
signtool verify /v /pa path\to\msi\msi.msi
pause
Hope that helps
. If not, please do query and I'll see if I can clarify.