From some time we know it is possible to bypass the 4 digits code on iMacs, mac air and MacBook pro using a version Arduino . using the Teensy Arduino. this device allow use brute force to run all possible combinations numbers between 0000 and 9999 . It is quite slow but easy to use this hardware combined by software and hardware . the code to use is done and available on github for free to try . some developers also made new version for Teensy Tutorial – Macbook iCloud EFI 4 pin unlock.
you can buy Teensy Arduino on ebay , it not expensive usb device . Also some people already sell Teensy version patched with the brute force code.
This device costs about $30 on eBay and plugs into the USB port on your mac
how to config your software
WORKING METHOD FOR BYPASSING APPLE EFI FIRMWARE PASSWORD / ICLOUD LOCK
Unlock ICloud Locked Macbook Pro, MacBook Air, iMac , Mac Mini
Unlock ICloud Locked Macbook Pro, MacBook Air, Imac , Mac Mini