13 Chapter 13. Intrusion detection services Intrusion is a term describing undesirable activities. The objective of an intrusion might be to acquire information that a person is not authorized to have. It might be to gain unauthorized use of a system as a stepping stone for further intrusions elsewhere. It might also be to cause business harm by rendering a network, host system, or application unusable. Most intrusions follow a pattern of information gathering, attempted access, and then destructive attacks. Intrusion detection services (IDS) guards against these intrusions, providing protection against potential hackers.