When I try to install the USB driver on windows 8/8.1, I get an error message
Since Windows 8 the driver signature enforcement is enabled by default. To be able to install unsigned drivers this enforcement needs to be disabled. Windows has to restart for this procedure. Therefore, make sure you saved all opened work before continuing.
By following this guide windows will after the reboot visually the same as before. Though Windows 8/8.1 will behave the same as Windows 7 for installing an unsigned driver. This mode will only last until the next reboot but the installed drivers will not be deleted after a reboot. Therefore you have to enter this mode every time you want to install a new/different unsigned driver.
Boot into advanced startup
Open the “Run Command” by pressing “Windows Key” + “R”, then type ”shutdown.exe /r /o /f /t 00″ and press the “OK“ Button.
Startup settings for disabling driver enforcement
Click “Troubleshoot” in the list of options.
Click “Advanced options” among the "Troubleshoot" options.
Click “Startup Settings” on the “Advanced options” list.
Finally restart the Computer by clicking on the “Restart” Button.
Disable driver signature enforcement
After the restarting the OS you can choose the mode you like to boot in. To disable the driver signature enforcement choose here option 7 by pressing the function key “F7”.