An intrusion-detection system (IDS) is a software-based tool used to detect for crackers or other security breaches such as incoming shellcodes, viruses or trojan horses in a computer system or network.
Two main types of intrustion detection system exists:
... the town the population is spread out with 22.3% under the age of 18, 8.0% from 18 to 24, 31.0% from 25 to 44, 21.9% from 45 to 64, and 16.9% who are 65 years of age ...