How to Install an ATtiny Bootloader With Virtual USB
Shawn Hymel 
Install USB Drivers
Because micronucleus requires custom drivers based on libusb, many operating systems will need to have the custom drivers installed or perform some custom configuration. Find your operating system below and follow the instructions.
Windows
Unfortunately, Windows doesn't know what to do with the micronucleus bootloader on the ATtiny84. It comes up as an Unknown USB Device, so we'll fix that with a custom driver. Lucky for us, the micronucleus project already comes with one.
Plug in a USB micro cable from your computer to the USB micro breakout on the breadboard. Windows will likely tell you that no driver could be found.
Navigate to \
In the interface, select Unknown Device #1 from the dropdown menu, and make sure that libusb-win32 is selected for the driver.
Click Install Driver and let Zadig do its thing. Close out of Zadig once the installation is complete.
Mac
If you installed libusb from the previous section, you should be all set.
Linux
You have two choices. You can either run Arduino with root privileges in order to send data to an "unknown" USB device, or you can install a set of udev rules to allow regular users to upload programs. To install the udev rules, run the following commands:
cd \<micronucleus Directory>/commandline
sudo cp 49-micronucleus.rules /etc/udev/rules.d/