It will be a kind of security check, but the thing is that it should - must - be possible to choose if you want to have it, or not!
1. If the external drive runs without problems, you don't want to scan, because
2. it COULD happen that the scan messes up files on your drive.
3. Therefore you don't want to have a situation where you happen click to scan by mistake...
If something doesn't work as it should with the drive, then you can always run a scan, anyway.
For that you need no pop-up...