So 3 days ago I locked my Mac from my iPhone using Apple's Find My iPhone app. It asked me to enter a 4-digit passcode, which would be used to unlock the Mac. The only catch was that the passcode I put in had a typo in it. So, with a completely incapacitated MacBook Pro, I began to search for answers on my little iPhone. Most people suggested a PRAM reset, booting into the recovery drive, wiping the hard drive, most of which required me to boot into a secondary boot disk. So I tried as suggested, rebooting my computer and holding down Option. Find My Mac set an EFI firmware password on my Mac as well as the OS password! This disabled me from doing anything from the boot menu, which essentially meant I couldn't do anything. So as a last resort, I brought the Mac to the Apple Store, without a reservation because it was urgent. The employees put me on the waiting list rapidly, on which I waited for 30 minutes before their "top Genius" could see me. The top genius started out with zeroing out the hard drive. This I could have done myself on another computer, but he did it for me this time. It didn't matter though, because the EFI password remained unaffected. Seeing this, he tried to install a fresh copy of Lion from a LaCie Rugged FW800 drive they had. Again, the boot menu was locked away. Finally, the Genius took the computer to the magical land of "behind that wall that says Genius" to do some specialized work. This was an EFI firmware reset, which involved opening the bottom panel and doing some magickery of sorts. In the end, he handed my Mac back with all my data wiped clean and the EFI password gone. The data was not an issue because I had backed up my stuff onto my Time Capsule. So, I brought the laptop home and immediately I installed Snow Leopard on it. No EFI password, yay! Updated the Mac to 10.6.8 fine then installed the latest version of Lion. The install app finished downloading, and the computer restarted, but as it was booting up... ...the 4-digit passcode screen came up again. Frustrated, I tried everything including reinstalling Snow Leopard and booting from a Lion DVD that I burned as a failsafe. None of them could solve the problem. I gave a PRAM reset a go. Then magically, the passcode disappeared! I could install Lion again and everything! And the best part is that the Genius didn't charge me a thing. Awesome service. So, if you're ever stuck in a similar situation as me, remove the EFI password then do a PRAM reset.