Is it possible when we use someone's compiled version of bitcrack and they modified the source code like that "if addr is = 16jY7qLJnxb7CHZyqBP8qca9d51gAjyXQN email me xyz@hotmail.com and print reached end of keyspace" something like that 
So We do not know that we have solved the key. And does the compiler get the key without knowing us
So We do not know that we have solved the key. And does the compiler get the key without knowing us yes , compiled exe can do it ..... like Trojan Virus .....
but 0x8000000000000000 is very big number ....
we have no super GPUs to find #64 private key ....possibility very little