This question comes to mind after seeing "custom" Bitcoin addresses with some special string at the beginning of the address. They are generated in the same way Bitcoins are "mined", continually hashing with a nonce + password to get some desired output.
My question is, is it just as hard to find
[HLOWRLD]M9VveeBLcY4UC4vjpPs6rZtFBQE as it is to find
1FpUYCpM9V[HLOWRLD]4UC4vjpPs6rZtFBQE as it is to find
1FpUYCpM9VveeBLcY4UC4vjpPs6[HLOWRLD]? *Note the values in the digest not in brackets can be any value
The reverse to the question, given you have some insane computer, would it be easier to try to find the input for