The use of IDSs continues to grow in popularity. However, as the use of IDSs grow, attacks against them grow as well. In this article, we reviewed existing IDS technologies and showed you how to attack them. By understanding the weaknesses of IDSs, you can more appropriately implement them in your layered security policy. In addition, we showed how threats against IDSs and the changing network milieu of IPSec are combining to force the evolution of IDSs into host-based, strict anomaly detectors.