You probably could get a huge performance boost out of this method if you tweaked your PIN list a little. Most common PINs would be any combinations with all same numbers like 0000, 1111, 2222, 3333, etc. So you should probably try thous first then things like 1234, 1212, 4321, 6969. Because people like patterns and people are lazy and don't wan't to remember more than two numbers. Just my two cents.