If you see this message, it means that an app, service, or piece of hardware that you’re using has tried to load a driver, app, or other file that isn’t properly signed.
You might think of it like inviting someone to a enter a secure area and they bring a guest along. Even though you may be confident that the person you invited is safe, you’ll still want to confirm that their guest is as well.
Smart App Control knows that what you're using is safe but isn't able to make a confident prediction about the safety of the other file your app opened so it attempted to verify the publisher of that file by checking its signature. The file isn’t properly signed so Smart App Control has blocked it.
As a result, whatever functionality that file was supposed to provide isn’t going to work, even though the rest of the app may continue to work just fine.