Originally Posted by sscn
Say once run /root/Desktop/test.sh, I can copy /tmp/test.sh to replace it.
On a security note, copying a script from /tmp/ for root to execute would be a bad idea in a multi-user environment. It may provide an opportunity for someone to modify or replace the file, maybe even accidentally, and get their substitute executed by root.
Even if you're sure there are no possible other users, there's a very remote chance that some cron job could accidentally do the same thing.