Before installing a software package on a client via Remote Desktop, use the ARD Lock Screen command first, then install.
After installing the software, restart any client computers that are at the login window.
When installed at the login window, some packages installers will display a dialog which will allow the client to login as root even though the login window is still displayed. Because of this, you should restart the client computers when running a package installation task to prevent any unauthorized users from obtaining root access.