Computers have been used by organizations and businesses from the day of its inception. Later on, computers were networked to form the internet. However, for connecting to the internet, businesses often choose to form a local area network within their premises and this network is connected with the internet through gateways. Also, there have been issues regarding the security of computer systems and networks, as they are used to store sensitive information or communicate to relevant persons at distant locations. Moreover, there have been cyber crimes that have raised many questions regarding the safety of computer systems and networks. To understand the situation in a deeper way, you need to appreciate the way computers work. Computers are not the collection of tangible hardware that you can catch hold of. In fact, only the hardware components amount to nothing but some dead, fancy and costly mini toys. What puts life into the hardware and makes it work is the software. Now, among the software, the major one is the operating system. The job of an operating system, among many others, is to manage the resources for processes, applications and system requirements. It does so in a quiet manner, often at the back ground. The operating system has two components – the kernel and the shell. The kernel is mainly responsible for hardware management, and is regarded as the innermost layer of all software. The second layer is the shell. Users can access the shell and instruct the kernel what work to fetch from the hardware, and the kernel complies accordingly. If you want to save a file or send an email, what you basically do is to instruct the kernel through the shell (often you use other software for accessing the shell, although it is readily accessible at the command prompt) to make changes in the hardware voltages. You must have heard about the binary logic of 0 and 1 that controls a computer. This binary logic is nothing but two distinct voltage levels of 0 Volt and +5 Volt respectively. Changes in these levels, as in this particular case, will create patterns at a specific portion of your hard drive, and your file will be saved at a definite location. Off course, you don’t get a whiff of such complex processes that gets done within a second at the click of a mouse, but this is the naked picture. Now, if anyone wants or can access the shell of your computer system, either over a network or at the physical machine itself, and have the right skills, he can hack into your system and access all the files, see them, delete or modify them, download them, or even send emails and virtually every possible thing that can be done with a computer. In computer professionals’ parlance, persons executing these types of malicious activities are called crackers. They are the villains among the computer communities. However, the technology that empowers a hacker can also be used to trace back the hacker, provided one has the right tools and adequate knowhow of the subject. These experts are called the real hackers, who tests computer systems and networks to make them more secure and robust. Such tests, called the security analysis and network penetration tests, are not easy to perform and cannot be done only through theoretical knowledge. There are professional consultants who are experts in this domain and enterprises often end up hiring them.