Reproducing the effects of large-scale worm attacks in a laboratory setup in a realistic and reproducible manner is an important issue for the development of worm detection and defense systems. In this paper, we describe a worm simulation model we are developing to accurately model the large-scale spread dynamics of a worm and many aspects of its detailed effects on the network. We can model slow or fast worms with realistic scan rates on realistic IP address spaces and selectively model local detailed network behavior. We show how it can be used to generate realistic input traffic for a working prototype worm detection and tracking system, the Dartmouth ICMP BCC: System/Tracking and Fusion Engine (DIB:S/TRAFEN), allowing performance evaluation of the system under realistic conditions. Thus, we can answer important design questions relating to necessary detector coverage and noise filtering without deploying and operating a full system. Our experiments indicate that the tracking algorithms currently implemented in the DIB:S/TRAFEN system could detect attacks such as Code Red v2 and Sapphire/Slammer very early, even when monitoring a quite limited portion of the address space, but more sophisticated algorithms are being constructed to reduce the risk of false positives in the presence of significant "background noise" scanning.