Code doesn't work at a one-to-one relationship. You can write any number of different codes to the same end. Because of this, de-obfuscating code is very difficult. You can try using some de-obfuscation extensions like this one, but I wouldn't get my hopes up on getting legible code back. Also, if the hacker is smart, he'll have used a number of redirects and other measures to make sure you can't track him even if you de-obfuscated the code.
