Introduction of Ethical Hacking
Web applications bring with them new and significant security threats. Each application is different and may contain unique vulnerabilities. Most applications are developed in-house — many by developers who have only a partial understanding of the security problems that may arise in the code they are producing. New technologies have been developed that have introduced new possibilities for exploitation. Some categories of flaws have largely gone away as the result of changes made to web browser software.
The most serious attacks against web applications are those that expose sensitive data or gain unrestricted access to the back-end systems on which the application is running.
You should have enough knowledge about computer networks as well how computer works to start hacking . There are different types of hacking, and according to that type prerequisites might change. For instance, if you are going to deal with web hacking then some knowledge of web & web technologies ( html, php, sql..etc) is required. You might know that most of hacking is done on Linux so basic understanding of Linux is required.