This is the greatest case of false advertising I’ve seen since I sued the movie The Never Ending Story.

—Lionel Hutz The Simpsons

Your network is firewalled, your servers are locked down, and you feel good about the defensive posture of your environment. However, you do not yet have any idea about the actual attacks being launched against your systems. Are evil hackers using automated tools to scan your network and inventory all your services? Are malicious internal users attempting to break into your severs using known vulnerabilities to commit insider fraud? If they are, are they succeeding?

In order to find out the answers to these questions, you may turn to an Intrusion Detection System (IDS). An IDS is, at its most basic level, a program or host that looks for signs that a resource is being attacked.