Hacking is unauthorized use of computer and network resources. (The term "hacker" originally meant a very gifted programmer. In recent years though, with easier access to multiple systems, it now has negative implications.)
Hacking is a felony in the United States and most other countries. When it is done by request and under a contract between an ethical hacker and an organization, it's OK. The key difference is that the ethical hacker has authorization to probe the target.
We work with IBM Consulting and its customers to design and execute thorough evaluations of their computer and network security. Depending on the evaluation they request (ranging from Web server probes to all-out attacks), we gather as much information as we can about the target from publicly available sources. As we learn more about the target, its subsidiaries and network connectivity, we begin to probe for weaknesses.
Examples of weaknesses include poor configuration of Web servers, old or unpatched software, disabled security controls, and poorly chosen or default passwords. As we find and exploit vulnerabilities, we document if and how we gained access, as well as if anyone at the organization noticed. (In nearly all the cases, the Information Syhstems department is not informed of these planned attacks.) Then we work with the customer to address the issues we've discovered.
The number of really gifted hackers in the world is very small, but there are lots of wannabes.... When we do an ethical hack, we could be holding the keys to that company once we gain access. It's too great a risk for our customers to be put in a compromising position. With access to so many systems and so much information, the temptation for a former hacker could be too great -- like a kid in an unattended candy store.