Computer security (also known as cybersecurity or IT security) is information security as applied to computing devices such as computers and smartphones, as well as computer networks such as private and public networks, including the Internet.
The field covers all the processes and mechanisms by which computer-based equipment, information and services are protected from unintended or unauthorized access, change or destruction, and is of growing importance in line with the increasing reliance on computer systems of most societies worldwide.
A backdoor in a computer system, a cryptosystem or an algorithm, is a method of bypassing normal authentication, securing remote access to a computer, obtaining access to plaintext, and so on, while attempting to remain undetected. The backdoor may take the form of an installed program (e.g., Back Orifice), or could be a modification to an existing program or hardware device. A specific form of backdoor is a rootkit, which replaces system binaries and/or hooks into the function calls of an operating system to hide the presence of other programs, users, services and open ports. It may also fake information about disk and memory usage.
Source From : http://en.wikipedia.org/wiki/Computer_security
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