There has been a constant bombardment of worms over the internet recently. In some cases, the spread of these worms was pandemic. Worms have continued to threaten network security - creating unnecessary network data traffic causing network congestion - in addition to the payload they usually carry. In this book, we derive and simulate some deterministic models, under a novel concept, for estimating the propagation of a worm to vulnerable networks or/and computers through networks; and analyse, using the same concept, some known effects of worm propagation. We also derive some graphical models...