Complex sentence: This information is very useful to a hacker who is trying to crack a whole system--not just an email account or a bank accounty finding out everything a system does and has on it, the hacker can become an extremely powerful attacker.
Split into simpler sentences: This information is very useful to a hacker who is trying to crack a whole system--not just an email account or a bank account. By finding out everything a system does and has on it, the hacker can become an extremely powerful attacker.