In principle, only allow other peoples control your computer if you really trust them. If you really need to allow a stranger remote control your computer to support, you should not worry because you can observe what they do on your screen and you can reclaim the mouse whenever you want. Thus, the only thing you need to for safety is to keep an eye on their control if your computer contains sensitive data.
When you enter the serial number into UltraViewer, UltraViewer will encode the serial number-key that you entered in one-way encrypted, so hackers will not be able to decompile the serial-key you typed.