In my opinion certain kind of work is quite pointless and worthless, you will spend your resources and time on a work that has no value at all, in my opinion it's like some kind of virus that he mistakenly cracked to get your wallet or he wants to use your CPU to mine some coin.
I understand your concerns and I had them myself, but BitcoinWalletCracker is open source, it is a script written in PHP, I checked and it is free from malicious code.