When you connect your VBOX 3iS to a computer over serial, it is possible that the computer detects the unit as a mouse. If this happens, the cursor will start to move around the screen and click randomly.
To remedy this, you need to first power off the VBOX 3iS. Next you open the Device Manager on your computer, and open the Mice and other pointing devices menu. Find the new/extra mouse or trackpad that is listed and Disable it (do not uninstall it). This will prevent it from happening again.