The concept of Double MD5 Encryption is simple, you just need to make sure that do it right, here is an example code:

PHP:
<?php
$pass= "hackedpass123";
echo md5(md5($pass));

?>
This would return: 6983505b0cd56b410d49f486cfe125d0 and it's really difficult and in most cases impossible to crack this. General MD5 Hashes have the word/password there, but if you were to encrypt a password twice, the only way of finding that encryption is to double encrypt. It's really easy to install onto your original Script/Code