Security of IT systems centers on preventing and detecting the unauthorised access to or use of IT systems
or impairment of those systems. To achieve such security, modern organisations layer security defences in IT
systems to reduce the chance of a successful attack. This concept is known as defence-in-depth and seeks
to manage risk with multiple defensive strategies, so that if one layer of defence turns out to be inadequate,
another layer of defence will hopefully prevent a full breach. The multiple defence mechanisms layered across
an organisation’s network infrastructure protect data, networks, and users. A well-designed and implemented
defence-in-depth strategy can help system administrators identify internal and external attacks on a computer
system or network.