You're getting these warnings because your games don't have a code-signing certificate. To supress the warnings, you have to submit each game to Microsoft Security Intelligence (https://www.microsoft.com/en-us/wdsi/filesubmission). They will scan it within about 3 hours, and if clean the warnings will stop when people try to install your game.
Because your code isn't signed, you'll have to do this each time you update the game because it will have a different hash.
Another alternative is to provide a no-install version (.zip file) - it's good to give people a choice to play without installing.
Buying a signing certificate can be costly, so unfortunately you have some extra work to do as an unknown dev.