I guess hacking becomes a career after you get cough intruding in systems which are supposed to be of high security (or you get in jail 8-O).
Government agencies usually hire hackers (or make them work for free, who knows) to help them locate any vulnerabilities in the systems.
Maybe there are companies that hire hackers in order to offer services regarding intrusion and safety testing for company servers or something.
Yes, I have read about ex-hackers being employed by companies to test or improve security. However, as the majority of hacking is illegal I doubt you will find a good, comprehensive source of information.
If you are interested in internet security thought, there will be books and other information available to help you make a secure system.
Dear friend,
I mean,I want to learn about network security to protect our network.if we know hacking then only we can protect the servers and computers from the hacker attacks.please provide some useful books or websites.