Security risks have grown dramatically for Internet service providers because entire infrastructures are based on open standards systems. As a result, ISPs need to be able to quickly and accurately detect unauthorized changes and respond accordingly, in order to maximize security and minimize downtime.

Intrusion Detection Systems (IDS) remain relatively youthful, but in terms of development they are growing at an extraordinary rate.

Generally speaking, there are four different categories of intrusion detection systems—network instruction detection, system integrity verifiers, log file monitors, and deception systems.

Network intrusion detection systems (NIDS) monitor packets traversing the system in an attempt to discover anomalies, indicating that an intruder trying to break into a system, or worse—launch a distributed denial of service (DDoS) attack. NIDSs look for frequent connection requests to different ports to reveal port scans.

System integrity verifiers (SIV) monitor system files in an attempt to discover when an intruder changes the files—leaving behind a backdoor. A SIV may be capable of detecting changes in critical files, but these systems usually don't generate real-time alerts to network intruders.

Log file monitors (LFM) simply monitor log files generated across network services. LFMs also look for patterns and anomalies in log files that suggest an intruder is attacking the network.

The sole purpose of a deception system—known in the industry as decoys, fly traps and honeypots—is to lure an unsuspecting intruder into a network through well-known security holes and trap the intruder.

Whether you need a simple intrusion alert system and network anomaly reports, or need to defend your network against DDoS attacks, smurfing, ping floods and the like, it's a imperative that you prepare a line of defense today or risk having your business be exploited by some script kiddie tomorrow.

This directory and Quick Reference Chart are designed to introduce service providers to most ISP-friendly commercial IDS services and simplify the process of determining which security system is right for your business.